Move namespace Leaf.Core.Extensions.System to Leaf.Core.Extensions.

New methods: ThreadSafeUI.IsCanceledByUser(Exception).
New extensions:
SmtpClient.SendMailAsync(MailMessage, CancellationToken);
string.IsNullOrEmpty();
string.HasContent();
Task.Caf() = Task.ConfigureAwait(false);

Leaf.Core.sln.DotSettings

@@ -6,10 +6,12 @@
 	<s:Boolean x:Key="/Default/UserDictionary/Words/=_041F_043E_0442_043E_043A_043E_0431_0435_0437_043E_043F_0430_0441_043D_0430_044F/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/UserDictionary/Words/=_041F_043E_0442_043E_043A_043E_0431_0435_0437_043E_043F_0430_0441_043D_043E_0435/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/UserDictionary/Words/=_0422_043E_043A_0435_043D/@EntryIndexedValue">True</s:Boolean>
+	<s:Boolean x:Key="/Default/UserDictionary/Words/=_042D_043A_0437_0435_043C_043B_044F_0440/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/UserDictionary/Words/=_043B_043E_0433_0438_043D_043E_0432/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/UserDictionary/Words/=_043C_043D_043E_0433_043E_043F_043E_0442_043E_0447_043D_043E_0439/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/UserDictionary/Words/=_043C_043D_043E_0433_043E_043F_043E_0442_043E_0447_043D_0443_044E/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/UserDictionary/Words/=_043E_043F_0446_0438_043E_043D_0430_043B_044C_043D_0430_044F/@EntryIndexedValue">True</s:Boolean>
+	<s:Boolean x:Key="/Default/UserDictionary/Words/=_043F_0430_0442_0442_0435_0440_043D/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/UserDictionary/Words/=_043F_043E_043F_0430_043F_0430_044E_0442/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/UserDictionary/Words/=_043F_043E_0442_043E_043A_043E_0431_0435_0437_043E_043F_0430_0441_043D_043E_0433_043E/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/UserDictionary/Words/=_043F_043E_0442_043E_043A_043E_0431_0435_0437_043E_043F_0430_0441_043D_043E_0439/@EntryIndexedValue">True</s:Boolean>

Leaf.Core.sln.DotSettings.user

@@ -1,5 +1,6 @@
 <wpf:ResourceDictionary xml:space="preserve" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:s="clr-namespace:System;assembly=mscorlib" xmlns:ss="urn:shemas-jetbrains-com:settings-storage-xaml" xmlns:wpf="http://schemas.microsoft.com/winfx/2006/xaml/presentation">
 	<s:Boolean x:Key="/Default/CodeStyle/Naming/CSharpAutoNaming/IsNamingAutoDetectionCompleted/@EntryValue">True</s:Boolean>
+	<s:Boolean x:Key="/Default/CodeStyle/Naming/CSharpAutoNaming/IsNotificationDisabled/@EntryValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/CodeStyle/Naming/CSharpNaming/ApplyAutoDetectedRules/@EntryValue">True</s:Boolean>
 	<s:String x:Key="/Default/CodeStyle/Naming/CSharpNaming/AutoDetectedNamingRules/=Constants/@EntryIndexedValue">&lt;Policy Inspect="True" Prefix="" Suffix="" Style="AaBb"&gt;&lt;ExtraRule Prefix="Between" Suffix="" Style="AaBb" /&gt;&lt;/Policy&gt;</s:String>
 	<s:String x:Key="/Default/CodeStyle/Naming/CSharpNaming/AutoDetectedNamingRules/=EnumMember/@EntryIndexedValue">&lt;Policy Inspect="True" Prefix="" Suffix="" Style="AaBb" /&gt;</s:String>

Leaf.Core/Extensions/System/DateTimeExtensions.cs → Leaf.Core/Extensions/DateTimeExtensions.cs

@@ -1,7 +1,7 @@
 using System;
 using System.Globalization;
 
-namespace Leaf.Core.Extensions.System
+namespace Leaf.Core.Extensions
 {
     public static class DateTimeExtensions
     {

Leaf.Core/Extensions/System/ExceptionExtensions.cs → Leaf.Core/Extensions/ExceptionExtensions.cs

@@ -1,7 +1,7 @@
 using System;
 using System.Text;
 
-namespace Leaf.Core.Extensions.System
+namespace Leaf.Core.Extensions
 {
     /// <summary>
     /// Делегат, обрабатывающий исключение внутри нескольких исключений (объединённых).

Leaf.Core/Extensions/Net/SmtpClientExtensions.cs

@@ -0,0 +1,77 @@
+using System;
+using System.Net.Mail;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace Leaf.Core.Extensions.Net
+{
+     public static class SmtpClientExtensions
+    {
+         /// <summary>
+        /// Sends the specified message to an SMTP server for delivery as an asynchronous operation.
+        /// </summary>
+        /// <param name="client">
+        /// The <see cref="SmtpClient"/> instance.
+        /// </param>
+        /// <param name="message">The <see cref="MailMessage"/> to send.</param>
+        /// <param name="cancellationToken">The <see cref="CancellationToken"/> to monitor for cancellation requests.</param>
+        /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
+        /// <exception cref="ArgumentNullException">
+        /// <para><paramref name="client"/> is <see langword="null"/>.</para>
+        /// <para>-or-</para>
+        /// <para><paramref name="message"/> is <see langword="null"/>.</para>
+        /// </exception>
+        public static Task SendMailAsync(this SmtpClient client, MailMessage message, CancellationToken cancellationToken)
+        {
+            if (client == null) throw new ArgumentNullException(nameof(client));
+            if (message == null) throw new ArgumentNullException(nameof(message));
+            if (!cancellationToken.CanBeCanceled) return client.SendMailAsync(message);
+
+            var tcs = new TaskCompletionSource<object>();
+            var registration = default(CancellationTokenRegistration);
+            SendCompletedEventHandler handler = null;
+
+            handler = (sender, e) => {
+                if (e.UserState != tcs) 
+                    return;
+
+                try
+                {
+                    if (handler == null) 
+                        return;
+
+                    client.SendCompleted -= handler;
+                    handler = null;
+                }
+                finally
+                {
+                    registration.Dispose();
+
+                    if (e.Error != null)
+                        tcs.TrySetException(e.Error);
+                    else if (e.Cancelled)
+                        tcs.TrySetCanceled();
+                    else
+                        tcs.TrySetResult(null);
+                }
+            };
+
+            client.SendCompleted += handler;
+
+            try
+            {
+                client.SendAsync(message, tcs);
+                registration = cancellationToken.Register(client.SendAsyncCancel);
+            }
+            catch
+            {
+                client.SendCompleted -= handler;
+                registration.Dispose();
+                throw;
+            }
+
+            return tcs.Task;
+        }
+
+    }
+}

Leaf.Core/Extensions/System/NumberFormatExtensions.cs → Leaf.Core/Extensions/NumberFormatExtensions.cs

@@ -1,7 +1,7 @@
 using System.Globalization;
 using Leaf.Core.Extensions.String;
 
-namespace Leaf.Core.Extensions.System
+namespace Leaf.Core.Extensions
 {
     /// <summary>
     /// Расширения для форматирования чисел к виду с разделителем тысяч.

Leaf.Core/Extensions/String/StringExtensions.cs

@@ -32,6 +32,20 @@ public static bool IsWebLink(this string self, bool trim = false)
         /// <returns>Вернет <see langword="null"/> если строка равна <see cref="string.Empty"/>.</returns>
         public static string NullOnEmpty(this string self) => self == string.Empty ? null : self;
 
+        /// <inheritdoc cref="string.IsNullOrEmpty"/>
+        /// <summary>
+        /// Расширение для метода <see cref="string.IsNullOrEmpty"/>.
+        /// </summary>
+        /// <param name="self">Строка</param>
+        public static bool IsNullOrEmpty(this string self) => string.IsNullOrEmpty(self);
+
+        /// <summary>
+        /// Проверка строки на полезный контент.
+        /// </summary>
+        /// <param name="self">Строка</param>
+        /// <returns>Вернет <see langword="true" /> если строка не является <see langword="null"/>, пустой строкой и пробелами.</returns>
+        public static bool HasContent(this string self) => !string.IsNullOrWhiteSpace(self);
+
         /// <summary>
         /// Проверяет наличие слова в строке, аналогично <see cref="string.Contains(string)"/>, но без учета реестра и региональных стандартов.
         /// </summary>

Leaf.Core/Extensions/TaskExtensions.cs

@@ -0,0 +1,11 @@
+using System.Runtime.CompilerServices;
+using System.Threading.Tasks;
+
+namespace Leaf.Core.Extensions
+{
+    public static class TaskExtensions
+    {
+        public static ConfiguredTaskAwaitable Caf(this Task task) => task.ConfigureAwait(false);
+        public static ConfiguredTaskAwaitable<T> Caf<T>(this Task<T> task) => task.ConfigureAwait(false);
+    }
+}

Leaf.Core/Extensions/System/TimeSpanExtensions.cs → Leaf.Core/Extensions/TimeSpanExtensions.cs

@@ -2,7 +2,7 @@
 using System.Globalization;
 using System.Text;
 
-namespace Leaf.Core.Extensions.System
+namespace Leaf.Core.Extensions
 {
     /// <summary>
     /// Расширения при работе со временем.

Leaf.Core/Threading/ThreadSafeUI.cs

@@ -65,6 +65,13 @@ public abstract class ThreadSafeUI
         /// </summary>
         public bool IsCanceled => CancelToken.IsCancellationRequested;
 
+        /// <summary>
+        /// Возвращает истину если исключение является <see cref="OperationCanceledException"/> и <see cref="CancelToken"/> был отменен.
+        /// </summary>
+        /// <param name="ex">Исключение которое было брошено</param>
+        /// <returns>Вернет истину если работа была отменена пользователем через <see cref="CancelToken"/>.</returns>
+        public bool IsCanceledByUser(Exception ex) => ex is OperationCanceledException && IsCanceled;
+
         /// <summary>
         /// Создает потокобезопасную реализацию для работы с интерфейсом.
         /// </summary>