Maniphest - use subscribers framework properly

Summary: Fixes T5604. This should fix some random bugs, lets us move forward more easily, and all that good stuff about killing code debt.

Test Plan:
- Conduit method maniphest.createtask
  - verified creating user subscribed
  - verified subscription transaction
- Conduit method maniphest.update
  - verified subscribers set as specified to ccPHIDs parameter
  - verified subscription transaction
- Herald
  - verified herald rule to add subscriber worked
  - verified no subscribers removed accidentally
- edit controller
  - test create and verify author gets added IFF they put themselves in subscribers control box
  - test update gets set to exactly what user enters
- lipsum generator'd tasks work
- bulk add subscribers works
- bulk remove subscriber works
- detail controller
  - added myself by leaving a comment
  - added another user via explicit action
  - added another user via implicit mention
- task merge via search attach controller
- mail reply handler
  - add subscriber via ./bin/mail receive-test
  - unsubscribe via ./bin/mail receive-test

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T5604

Differential Revision: https://secure.phabricator.com/D10965

src/applications/maniphest/controller/ManiphestTransactionPreviewController.php

@@ -58,22 +58,19 @@ final class ManiphestTransactionPreviewController extends ManiphestController {
         }
         $transaction->setNewValue($value);
         break;
-      case ManiphestTransaction::TYPE_CCS:
+      case PhabricatorTransactions::TYPE_SUBSCRIBERS:
         if ($value) {
           $value = json_decode($value);
         }
         if (!$value) {
           $value = array();
         }
-        $phids = $value;
-
-        foreach ($task->getCCPHIDs() as $cc_phid) {
+        $phids = array();
+        foreach ($value as $cc_phid) {
           $phids[] = $cc_phid;
-          $value[] = $cc_phid;
         }
-
-        $transaction->setOldValue($task->getCCPHIDs());
-        $transaction->setNewValue($value);
+        $transaction->setOldValue(array());
+        $transaction->setNewValue($phids);
         break;
       case ManiphestTransaction::TYPE_PROJECTS:
         if ($value) {