Allow users to "Edit a Copy" when trying to edit a panel they don't own

Summary:
Fixes T5167. When clicking "Edit" on a dashboard panel you don't own, the UI now allows you to make a copy instead.

As a bonus, fixes T5259.

Test Plan: See screenshots.

Reviewers: chad

Reviewed By: chad

Subscribers: epriestley

Maniphest Tasks: T5259, T5167

Differential Revision: https://secure.phabricator.com/D9505

src/applications/dashboard/controller/PhabricatorDashboardManageController.php

@@ -15,6 +15,10 @@ final class PhabricatorDashboardManageController
     $id = $this->id;
     $dashboard_uri = $this->getApplicationURI('view/'.$id.'/');
 
+    // TODO: This UI should drop a lot of capabilities if the user can't
+    // edit the dashboard, but we should still let them in for "Install" and
+    // "View History".
+
     $dashboard = id(new PhabricatorDashboardQuery())
       ->setViewer($viewer)
       ->withIDs(array($this->id))