Switch Calendar to EditEngine
Ref T9275. This throws away the old EditController and switches fully to EditEngine.
There's still some sketchy behavior (particularly, no JS stuff yet) but I think all the basics work properly.
Test Plan: Created and edited events via EditEngine, everything seemed to work alright.
Reviewed By: chad
Maniphest Tasks: T9275
Differential Revision: https://secure.phabricator.com/D16283