Summary: Begin converting Conpherence to ModularTransactions, this converts title, topic, and picture to use modular transactions. Participants seems hairy so I'll do that in another diff
Test Plan: Create a room with a topic, change room name, topic. Add people, remove people. Set a room image. Unset topic.
Reviewers: epriestley
Reviewed By: epriestley
Subscribers: Korvin
Differential Revision: https://secure.phabricator.com/D17668
