R1:3a8eb28a074f

Send basic email from new ApplicationTransaction editor

Summary: Ref T2222. Adds basic support for email.

Test Plan: Received an email via `/editpro/`.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2222

Differential Revision: https://secure.phabricator.com/D8303