Improve messaging of special policy rules in applications

Summary: Ref T603. When the user encounters an action which is controlled by a special policy rule in the application, make it easier for applications to show the user what policy controls the action and what the setting is. I took this about halfway before and left a TODO, but turn it into something more useful.

Test Plan: See screenshots.

Reviewers: btrahan, chad

Reviewed By: chad

CC: chad, aran

Maniphest Tasks: T603

Differential Revision: https://secure.phabricator.com/D7265

src/applications/policy/controller/PhabricatorPolicyExplainController.php

@@ -63,8 +63,14 @@ final class PhabricatorPolicyExplainController
       $auto_info = phutil_tag('ul', array(), $auto_info);
     }
 
+    $capability_name = $capability;
+    $capobj = PhabricatorPolicyCapability::getCapabilityByKey($capability);
+    if ($capobj) {
+      $capability_name = $capobj->getCapabilityName();
+    }
+
     $content = array(
-      pht('Users with the "%s" capability:', "Can View"),
+      pht('Users with the "%s" capability:', $capability_name),
       $auto_info,
     );