R1:a13390a919a2

Flags on mobile, fix some filter-css

Summary: Sets device flag on mobile, cleans up filter css a bit.

Test Plan: Tested filters on homepage, maniphest, flags, uiexamples.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D5559