[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