Storage rework + fixes

[Krakenied]

TODO:

• test storage rework (mysql)
• test storage rework (yaml)
• create copy for invalid yaml files on save
• docs
• fix isCancelled() on 1.8

[14:22:48 WARN]: [Quests] Task #1272 for Quests v3.15.2-3185f28 generated an exception
java.lang.NoSuchMethodError: org.bukkit.scheduler.BukkitTask.isCancelled()Z
        at com.leonardobishop.quests.bukkit.scheduler.bukkit.BukkitWrappedTask.isCancelled(BukkitWrappedTask.java:25) ~[?:?]
        at com.leonardobishop.quests.bukkit.runnable.QuestsAutoSaveRunnable.forceSave(QuestsAutoSaveRunnable.java:82) ~[?:?]
        at com.leonardobishop.quests.bukkit.runnable.QuestsAutoSaveRunnable.run(QuestsAutoSaveRunnable.java:36) ~[?:?]
        at org.bukkit.craftbukkit.v1_8_R3.scheduler.CraftTask.run(CraftTask.java:59) ~[server.jar:git-iSpigot-PaperEdition]
        at org.bukkit.craftbukkit.v1_8_R3.scheduler.CraftScheduler.mainThreadHeartbeat(CraftScheduler.java:410) ~[server.jar:git-iSpigot-PaperEdition]
        at net.minecraft.server.v1_8_R3.MinecraftServer.B(MinecraftServer.java:1038) ~[server.jar:git-iSpigot-PaperEdition]
        at net.minecraft.server.v1_8_R3.DedicatedServer.B(DedicatedServer.java:523) ~[server.jar:git-iSpigot-PaperEdition]
        at net.minecraft.server.v1_8_R3.MinecraftServer.A(MinecraftServer.java:948) ~[server.jar:git-iSpigot-PaperEdition]
        at net.minecraft.server.v1_8_R3.MinecraftServer.run(MinecraftServer.java:835) ~[server.jar:git-iSpigot-PaperEdition]
        at java.lang.Thread.run(Thread.java:750) ~[?:1.8.0_422]

TODO to be moved to another PR:

• storing preferences - tracked quest id
• menu rework
• placeholders support in menus (for example cancel gui)
• make hidden option hide the quest from more menus
• count instead of bool Number of times you’ve completed quests  #739 + yaml migrator