Rework desktop header

Summary: Removes the glow icons and uses a hover change. Fixes phantom anchors.

Test Plan: Review in Chrome at various sizes (phone tablet). Check that icons still work. Check that mobile menus render when clicked.

Reviewers: epriestley, btrahan

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2876

Differential Revision: https://secure.phabricator.com/D5549