Add role=dialog to all dialogs

Summary: Seen some complaints about usability here, adding role=dialog to improve when these trigger.

Test Plan: Turn on Voiceover, tab over to log out link, here proper dialog title and text before highlighted submit button.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D15993

src/view/AphrontDialogView.php

@@ -276,6 +276,7 @@ final class AphrontDialogView
     $attributes = array(
       'class'   => implode(' ', $classes),
       'sigil'   => 'jx-dialog',
+      'role'    => 'dialog',
     );
 
     $form_attributes = array(