Add Editor-based mail stamps: actor, via, silent, encrypted, new, mention, self-actor, self-mention
Summary: Ref T13053. Adds more mail tags with information available on the Editor object.
Test Plan: Banged around in Maniphest, viewed the resulting mail, all the stamps seemed to align with reality.
Reviewers: amckinley
Reviewed By: amckinley
Maniphest Tasks: T13053
Differential Revision: https://secure.phabricator.com/D18995