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
ReleephRequestStatus

Summary: This is just a bit of gardening in order to make the responsive-UI diff easier; I'll be putting `getColorFor($status)` type things in this class, following the pattern in `ManiphestTaskStatus`.

Test Plan: Poke around Releeph.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D5893