Allow Conpherence room images up to 200px

Summary: Provide higher resolution for Conpherence room images. Fixes T11728

Test Plan:
Upload a new photo, see it pulls in 200px image as background.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Maniphest Tasks: T11728

Differential Revision: https://secure.phabricator.com/D16659