R1:b3fa9d0c2f42

Modernize Diffusion "change" view

Summary:
- Kicks it out to full width.
- More useful header/crumbs/properties/actions (needs some more work).
- Works for public repositories.
- Fix a bug where the "rX" crumb would lose the branch you're on.

Test Plan: See screenshot.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D7063