Move Files editing and commenting to EditEngine

Summary:
Ref T11357. This moves editing and commenting (but not creation) to EditEngine.

Since only the name is really editable, this is pretty straightforward.

Test Plan: Renamed files; commented on files.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T11357

Differential Revision: https://secure.phabricator.com/D17611