R1:9bda03dbceed

Conpherence - add isRoom column to thread table

Summary: Fixes T7583. We also add `key_room`, which uses isRoom and dateModified since a very common view of rooms is going to be ordered by last updated.

Test Plan: made the conpherence view controller query specify `withIsRoom(true)` and `withIsRoom(false)`. The former made the controller correctly 404 while the latter had no change in functionality.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T7583…