Lockdown tool directory editing to administrators

Summary:
Someone has "defaced" secure.phabricator.com with a helpful suggestion that I
actually do this; fair enough. :P

Test Plan:
Logged in as myself, unable to edit directory information. Logged out, logged in
as admin, was able to edit directory information.

I need to fix some more CSS stuff since some of these tabs render out hideous in
the admin background, but I can followup with that.

Reviewed By: tuomaspelkonen
Reviewers: aran, jungejason, tuomaspelkonen
Commenters: aran
CC: aran, tuomaspelkonen, epriestley
Differential Revision: 296

src/applications/repository/controller/github-post-receive/PhabricatorRepositoryGitHubPostReceiveController.php

@@ -20,6 +20,10 @@
 class PhabricatorRepositoryGitHubPostReceiveController
   extends PhabricatorRepositoryController {
 
+  public function shouldRequireAdmin() {
+    return false;
+  }
+
   public function shouldRequireLogin() {
     return false;
   }