Move mail handling to proper mailtemplate DB.

[heyitsbench]

Currently grabbing strings from acore_string. I don't think this will work for a gendered locale like esES/esMX, plus it should just be using the proper DBC it eventually would use.

[heyitsbench]

Entries inserted in 2417538. acore_string entries still present for now since functionality is not moved over yet, that is still todo.