Make Diffusion Herald emails thread with Audit emails
Summary:
- Users may elect to receive an initial notification about a commit; allow it to be replied to in order to interact with the object.
- Share thread headers between emails.
- Add the "REPLY HANDLER ACTIONS" section to both emails.
Test Plan:
- Used "reparse.php --herald" to trigger herald emails, verified reply-to and email body.
- Made audit comments, verified body.
Reviewers: btrahan
Reviewed By: btrahan
CC: aran, epriestley
Maniphest Tasks: T904
Differential Revision: https://secure.phabricator.com/D1762