Allow configuration options to be locked

Summary: Some config shouldn't reasonably be edited from the web interface because it immediately torpedoes the install if you make a mistake. Block edits to "locked" config.

Test Plan: Tried to edit locked config, got denied. Viewed locked config on edit and list screens.

Reviewers: codeblock, btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2255

Differential Revision: https://secure.phabricator.com/D4320

src/applications/config/controller/PhabricatorConfigGroupController.php

@@ -91,6 +91,10 @@ final class PhabricatorConfigGroupController
         $item->addIcon('edit-grey', pht('Default'));
       }
 
+      if ($option->getLocked()) {
+        $item->addIcon('lock', pht('Locked'));
+      }
+
       $list->addItem($item);
     }