Restore some missing features from Maniphest mail

Summary:
Ref T2217. Fixes two issues:

1. The "task created" email didn't include the task description, but should.
2. We were treaging the "status" event as the "create", but that's kind of a mess. Treat the "title" event as the "create" instead. This makes initial emails say "[Created]".

Test Plan: Created some tasks, got better emails.

Reviewers: btrahan, chad

Reviewed By: chad

CC: aran

Maniphest Tasks: T2217

Differential Revision: https://secure.phabricator.com/D7115