Update Conpherence to use EditEngine

Summary: Moves Conpherence to use EditEngine. This removes the "First Message" field, but I think that's ok until we have direct messaging of some sort, then maybe have built-ins cover that case.

Test Plan:

• Visit /new/ and /edit/ for creating new rooms.
• Edit a room in full conpherence
• Edit a room in durable column
• grep for METADATA calls

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Maniphest Tasks: T11729

Differential Revision: https://secure.phabricator.com/D16677