Conpherence - Implement edit rules for rooms

Summary: Fixes T7586. If you can't edit a room, the pertinent UI is greyed out. One exception is the title of the room in the full viewer; this crumb is not disabled as it would be hard to read. Otherwise though, everything is disabled nicely.

Test Plan: tried to add participants when I wasn't allowed to and got an error. added participants otherwise okay. tried to edit title when i wasn't allowed and got an error. otherwise okay. left conpherence threads / rooms successfully.

Reviewers: epriestley, chad

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T7586

Differential Revision: https://secure.phabricator.com/D12161