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

src/applications/diffusion/controller/DiffusionDiffController.php

@@ -2,6 +2,10 @@
 
 final class DiffusionDiffController extends DiffusionController {
 
+  public function shouldAllowPublic() {
+    return true;
+  }
+
   public function willProcessRequest(array $data) {
     $data = $data + array(
       'dblob' => $this->getRequest()->getStr('ref'),