Conpherence - add icon-based room switcher to durable column view

Summary: Ref T7380. This does the most basic thing ever and sticks up to 6 icons in there.

Test Plan: clicked the icons and noted new conpherences loaded in nicely

Reviewers: epriestley, chad

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T7380

Differential Revision: https://secure.phabricator.com/D12037