Fix 'Transcript' links in Differential

Summary:
add filtering for MetaMTA transcripts, add Herald
transcripts, also fixed PhabricatorObjectHandleData to support commits.
Note that paging in the transcripts pages will be in a different diff.

Test Plan:
test the transcripts for both MetaMTA and Herald.

Reviewed By: epriestley
Reviewers: epriestley, tuomaspelkonen
CC: jungejason, epriestley
Differential Revision: 114

src/applications/differential/controller/revisionview/DifferentialRevisionViewController.php

@@ -313,6 +313,12 @@ class DifferentialRevisionViewController extends DifferentialController {
       'href'  => "/mail/?phid={$revision_phid}",
     );
 
+    $links[] = array(
+      'class' => 'transcripts-herald',
+      'name'  => 'Herald Transcripts',
+      'href'  => "/herald/transcript/?phid={$revision_phid}",
+    );
+
     return $links;
   }