Add profile images to Repositories

Summary: Builds out some images to use to identify repositories. Fixes T12825.

Test Plan:
Try setting custom, built in, and null images.

{F4998175}

{F4998192}

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Maniphest Tasks: T12825

Differential Revision: https://secure.phabricator.com/D18116

src/applications/diffusion/application/PhabricatorDiffusionApplication.php

@@ -140,6 +140,8 @@ final class PhabricatorDiffusionApplication extends PhabricatorApplication {
           $this->getEditRoutePattern('edit/') =>
             'DiffusionCommitEditController',
         ),
+        'picture/(?P<id>[0-9]\d*)/'
+          => 'DiffusionRepositoryProfilePictureController',
       ),
     );
   }