Use sprites for (nearly) all application icons

Summary: Sprites for everyone.

Test Plan: Loaded `/applications/`.

Reviewers: btrahan, chad, vrana

Reviewed By: vrana

CC: aran

Maniphest Tasks: T1569

Differential Revision: https://secure.phabricator.com/D3280

src/applications/diffusion/application/PhabricatorApplicationDiffusion.php

@@ -26,8 +26,8 @@ final class PhabricatorApplicationDiffusion extends PhabricatorApplication {
     return '/diffusion/';
   }
 
-  public function getIconURI() {
-    return celerity_get_resource_uri('/rsrc/image/app/app_diffusion.png');
+  public function getAutospriteName() {
+    return 'diffusion';
   }
 
   public function getHelpURI() {