Allow arc project and branch showing up in diff emails

Summary: Add the arc project and branch fields in emails for revisions under review. I am not quite sure why we only show them for changes which is already accepted or needs revision. It would be nice to have them for changes under review too.

Test Plan: Create a new revision and check email

Reviewers: epriestley, lifeihuang, JoelB, Blessed Reviewers

Reviewed By: epriestley

CC: Korvin, epriestley, aran

Differential Revision: https://secure.phabricator.com/D8035