Add sidenav back to workboards

Summary: This is still reasonably functional and useful to people, and we don't have better mechanics to offset the change.

Test Plan: New Workboard, set Workboard color, test mobile, desktop.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D16964