R1:81f42b834366

Align sidenavs better, use sky to highlight

Summary: Simplifies the UI here by removing various borders, instead using just background colors and better alignment.

Test Plan: Test instances, settings, home, projects, workboards.

Reviewers: epriestley

Reviewed By: epriestley

Spies: Korvin

Differential Revision: https://secure.phabricator.com/D18488