[Redesign] Move to light header by default
Summary: This should default to light, also made the icons on the dark headers more transparent.
Test Plan: Tested light, dark, blue, blindigo, and default.
Reviewers: btrahan, epriestley
Reviewed By: epriestley
Subscribers: epriestley, Korvin
Differential Revision: https://secure.phabricator.com/D13306