Expand SendBetterMail merge field functionality to support cross-object merge fields

[JnsMT]

Building on, brace yourself, a 15 year old idea, I've extended the default SendBetterMail's email template functionality to also support cross-object fields, eliminating the need to manually insert the values or trash the data model with formula fields not needed elsewhere. The new feature keeps the default merge fields syntax with {{{field}}} and adds the cross-object syntax ###field### to prevent confusion and errors during the standard merging process.

All you need to know is the field path thats also used in SOQL queries, for instance if your Email templates source object is Case and you want to retrieve the associated accounts name, you insert the following into the template:
###Account.Name###

The code uses a single query to fetch all fields inserted into the template and automatically formats Date and Datetime fields in the running users default format.