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
42a0229a52