R1:752055a45c16

Update mobile menu icons

Summary: Simplify the look of the mobile menu, provide active states for the menu icons.

Test Plan: iOS Simulator and Chrome.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2426

Differential Revision: https://secure.phabricator.com/D5189