s/TMail/Mail ; fix history function

Hi @auxesis 

This will take care of both issues I've raised :)
* it gets rid of TMail
* the history function works for @TimCorcoran's ticket (RT1886790)
As it turns out after a looooong dive down the rabbit hole the content of this task is upsetting the Mail.new function. See the below "fix":
https://github.com/bulletproofnetworks/roust/blob/remove_tmail/lib/roust.rb#L551-L552

Feedback will be most welcome :)