Switch Calendar to EditEngine

Summary:
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.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T9275

Differential Revision: https://secure.phabricator.com/D16283