R1:bd350abbe91c

Probably added app menu for mobile

Summary:
Messy POC. I hope I did this one right :P

Refs T2014

Test Plan: Switched browser forcefully into `device-phone`, saw filters in the menu top right. Browsed around Differential in desktop mode, nothing was broken, I think.

Reviewers: epriestley, chad, btrahan

CC: aran, Korvin

Maniphest Tasks: T2014

Differential Revision: https://secure.phabricator.com/D5693