Add a "Last Edited" property to Wiki pages

Summary:
Ref T13164. See PHI797. The last edit is available in the page header, but it's not precise (just says "180 days ago") and a little weird (it's unusual for us to put that kind of information in the header).

Add a precise timestamp to the footer for now. I'd imagine re-examining this the next time Phriction gets some UI work and maybe trying to integrate timeline/transactions more cleanly (see also T1894).

Test Plan: Looked at a wiki page, then edited it. Saw precise "Last Edit" timestamp adjacent to "Last Author".

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13164

Differential Revision: https://secure.phabricator.com/D19560

src/applications/phriction/controller/PhrictionDocumentController.php

@@ -254,7 +254,8 @@ final class PhrictionDocumentController
     PhrictionContent $content,
     $slug) {
 
-    $viewer = $this->getRequest()->getUser();
+    $viewer = $this->getViewer();
+
     $view = id(new PHUIPropertyListView())
       ->setUser($viewer)
       ->setObject($document);
@@ -263,6 +264,10 @@ final class PhrictionDocumentController
       pht('Last Author'),
       $viewer->renderHandle($content->getAuthorPHID()));
 
+    $view->addProperty(
+      pht('Last Edited'),
+      phabricator_datetime($content->getDateCreated(), $viewer));
+
     return $view;
   }