Conpherence - introduce ConpherenceThreadManager

Summary:
Ref T7014. Fixes T7473. This adds a class to handle thread state about what thread is loaded and what transaction we've seen last. It is deployed 100% in the durable column and only partially deployed in the regular view. Future diff(s) should clean up regular view. Note ConpherenceThreadManager API might change a bit at that time.

Also includes a bonus bug fix so logged out users can't toggle this column

Test Plan: tried to use durable column while logged out and nothing happened. sent messages, aphlict-received messages, added people, and changed title from both views

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T7473, T7014

Differential Revision: https://secure.phabricator.com/D12029