Summary: First pass here, still needs some UI work (maybe? tablets?). Getting it out to see if implementation is corrrect. Test Plan: Shrink Maniphest task on Chrome, see new UI. Toggle menu. Test on iOS. Reviewers: epriestley, btrahan Reviewed By: epriestley CC: aran, Korvin Differential Revision: https://secure.phabricator.com/D5631