Make EditEngine form for Calendar Events almost fully-functional

Summary:
Ref T9275. This still has a number of rough edges and other minor problems (no JS on the controls, some date handling control bugs) but I'll smooth those over in future changes.

It does make all the editable transaction types available from EditEngine, technically speaking.

Test Plan: Created and edited events with the "pro" controller, which mostly worked.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T9275

Differential Revision: https://secure.phabricator.com/D16281