Port Differential mail features forward to transactions
Summary:
Ref T2222. Brings the major mail features (affected files, patches) forward.
This drops some of the minor integrations which just show object state (like "Maniphest Tasks") since I think they're not very important. I'll put them back if users miss them.
Test Plan: Sent mail with inline/attached patches.
Reviewers: btrahan
Reviewed By: btrahan
CC: aran
Maniphest Tasks: T2222
Differential Revision: https://secure.phabricator.com/D8459