Add layout roles and CSS rules for devices for Conpherence

Summary: Currently, `/conpherence/` shows the widget panel on devices. Make it show the thread list instead.

Test Plan: {F38099}

Reviewers: btrahan

Reviewed By: btrahan

CC: aran, chad

Maniphest Tasks: T2421

Differential Revision: https://secure.phabricator.com/D5505