Dark sidebar everywhere

Summary:
First pass at testing out a dark sidebar everywhere. Wanting feedback with real test time before implementing before commiting.

Thoughts

• Aligns with Mobile, Tablet UI experience.
• Creates 'application' feel on Desktop.
• Begins to make Phabricator feel like a branded UI.

Cons

• Probably contensious visually.

TODO:

• Update diff view sidebar.
• Make breadcrumbs appear above content area, not above nav.
• Change background texture on crumbs to match table headers.

Test Plan: Testing Nav with fellow co-workers.

Reviewers: epriestley, btrahan

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D4427