Clean up more Quicksand

Summary: Creates a background that renders inside the Quicksand frame, through sorcery.

Test Plan: Turn on Quicksand, visit lots of pages. See correct background colors. This probably blows something up I'm not testing.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D16642

src/applications/config/controller/PhabricatorConfigCacheController.php

@@ -37,7 +37,7 @@ final class PhabricatorConfigCacheController
       ->setCrumbs($crumbs)
       ->setNavigation($nav)
       ->appendChild($content)
-      ->addClass('white-background');
+      ->addFrameClass('white-background');
   }
 
   private function renderCodeBox() {