ReleephRequest xactions

Summary:
Migrate to PhabricatorApplicationTransactions (ReleephRequestTransactions applied by ReleephRequestTransactionalEditor, instead of ReleephRequestEvents created by ReleephRequestEditor) and migrate all the old events into transactions. Email is supported in the standard way (no more ReleephRequestMail) as well.

This also collapses the Releeph request create and edit controllers into one class, as well as breaking everyone's subject-based mail rules by standardising them (but which should be more easily filtered by looking at headers.)

Test Plan:

• Make requests, then pick them.
• Pick and revert the same request so that discovery happens way after arc has told Releeph about what's been happening.
• Try to pick something that fails to pick in a project with pick instructions (and see the instructions are in the email.)
• Load all of FB's Releeph data into my DB and run the storage upgrade script.
• Request a commit via the "action" in a Differential revision.

Reviewers: epriestley

Reviewed By: epriestley

CC: epriestley, aran, Korvin, wez

Maniphest Tasks: T3092, T2720

Differential Revision: https://secure.phabricator.com/D5868