R1:8544d0d00f08

Implement "Edit Members" and "Join/Leave" with real ApplicationTransactions

Summary:
Ref T4379. Projects has been partially converted to ApplicationTransactions, but the rough state of the world is that all the //storage// is modern, but most of the stuff on top isn't yet. Particularly, there's a `PhabricatorProjectEditor` which is //not// a subclass of `PhabricatorApplicationTransactionEditor`, but which fakes its way through writing reasonable data into modern storage.

This introduces a real…