Add support for playing sounds

Summary:
Ref T5369. New HTML5 version without flash dependencies.

This doesn't play any sounds.

Test Plan: Did not play any sounds.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: joshuaspence, epriestley

Maniphest Tasks: T5369

Differential Revision: https://secure.phabricator.com/D9535

src/applications/celerity/controller/CelerityResourceController.php

@@ -125,6 +125,7 @@ abstract class CelerityResourceController extends PhabricatorController {
       'woff2' => 'font/woff2',
       'eot' => 'font/eot',
       'ttf' => 'font/ttf',
+      'mp3' => 'audio/mpeg',
     );
   }