[Tails-dev] [review'n'merge:1.4] feature/remove-msmtp-mutt

Hi,

this branch removes msmtp and mutt, as proposed by sycamoreone, and
decided on this list last month. Thanks to sycamoreone for the initial
version of the branch that I've built upon.

Candidate for Tails 1.4.

Cheers,
--
intrigeri