R1:20035fe9a8ed

Update Phabricator header to use FontAwesome

Summary: Updates header to use font-icons instead of images.

Test Plan: Test desktop and mobile layouts, Chrome, FF, Safari, IE.

Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D10930