R1:fcb728653312

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…