R1:85de4419a5f1

Conpherence - add storage for view / edit / join policy

Summary: Ref T7582. Also adds the basic logic for "rooms" implementation. Also makes sure we use the initializeNewThread method as appropriate.

Test Plan: made a new conpherence and it worked!

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T7582

Differential Revision: https://secure.phabricator.com/D12103