Conpherence - paginate thread list

Summary: this is D5750 but just the conpherence part. fixes a few random conpherence bugs / quirks as well. Also messes with ApplicationTransactionEditor to expose the xactions so Conpherence doesn't over-update participation rows. Fixes T2429.

Test Plan: set LIMIT to 3. verified I could scroll down all conpherences. next, picked a conpherence "in the middle" to load. verified I could page up and down. next, picked a conpherence in the middle then had another user update that conpherence. verified as I paged up the conpherence re-loaded properly selected

Reviewers: epriestley

Reviewed By: epriestley

CC: chad, aran, Korvin, vrana

Maniphest Tasks: T2429

Differential Revision: https://secure.phabricator.com/D5783

src/applications/conpherence/controller/ConpherenceViewController.php

@@ -50,6 +50,9 @@ final class ConpherenceViewController extends
         ->setBeforeTransactionID($before_transaction_id);
     }
     $conpherence = $query->executeOne();
+    if (!$conpherence) {
+      return new Aphront404Response();
+    }
     $this->setConpherence($conpherence);
 
     $participant = $conpherence->getParticipant($user->getPHID());