Provide link to all rooms when on mobile Conpherence

Summary: There isn't any link back to all your joined rooms when on mobile, add it here.

Test Plan: Pull up mobile, click on menu, see list of threads, click on other room.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D16717