Extend PHUITheme to include Profile Nav

Summary: Reasonable first pass, removes the "light" header, due to pain of upkeep. Reinforces UI color into the Profile Nav (and later likely dropmenu hovers). Most of this is reasonably easy to maintain now, but I may do a more accurate color pass after I get some more time together with it. For now this feels pretty good if you're developing in a different color UI.

Test Plan:
Switch between all the colors, hover over all the states.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D15120