Implement ApplicationSearch in Files

Summary: Ref T2625. Ref T1163. A couple of small generalization nudges, but this is almost entirely straightforward.

Test Plan: Executed various File queries.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T1163, T2625

Differential Revision: https://secure.phabricator.com/D6091

src/applications/paste/controller/PhabricatorPasteController.php

@@ -14,7 +14,7 @@ abstract class PhabricatorPasteController extends PhabricatorController {
 
     id(new PhabricatorPasteSearchEngine())
       ->setViewer($user)
-      ->addNavigationItems($nav);
+      ->addNavigationItems($nav->getMenu());
 
     $nav->selectFilter(null);