Make the admin view look better, and fix a minor Chrome CSS glitch

Summary:

• Provide a red version of the logo for the admin view.
  • Make selected tabs in the admin view look correct.
  • Fix a Chrome styling issue where the username and "settings" would have

weird offsets.

Test Plan:
Loaded Phabricator in chrome and clicked around tabs of an admin interface.
Hovered over logo.

Reviewed By: jungejason
Reviewers: cadamo, jungejason, tuomaspelkonen, aran
CC: aran, epriestley, jungejason
Differential Revision: 371