Update Maniphest for modular transactions

Summary: Ref T12671. This modernized Maniphest transactions to modular transactions.

Test Plan:
- Create Task
- Edit Task
- Raise Priority
- Change Status
- Merge as a duplicate
- Create Subtask
- Claim Task
- Assign Project
- Move on Workboard
- Set a cover image
- Assign story points
- Change story points
- Generate lots via lipsum
- Bulk edit tasks
- Leave comments
- Award Token

I'm sure I'm missing something.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: hazelyang, Korvin

Maniphest Tasks: T12671

Differential Revision: https://secure.phabricator.com/D17844

src/applications/project/controller/PhabricatorProjectCoverController.php

@@ -36,7 +36,7 @@ final class PhabricatorProjectCoverController
     $xactions = array();
 
     $xactions[] = id(new ManiphestTransaction())
-      ->setTransactionType(ManiphestTransaction::TYPE_COVER_IMAGE)
+      ->setTransactionType(ManiphestTaskCoverImageTransaction::TRANSACTIONTYPE)
       ->setNewValue($file->getPHID());
 
     $editor = id(new ManiphestTransactionEditor())

src/applications/project/controller/PhabricatorProjectMoveController.php

@@ -153,10 +153,11 @@ final class PhabricatorProjectMoveController
     $xactions = array();
     if ($pri !== null) {
       $xactions[] = id(new ManiphestTransaction())
-        ->setTransactionType(ManiphestTransaction::TYPE_PRIORITY)
+        ->setTransactionType(ManiphestTaskPriorityTransaction::TRANSACTIONTYPE)
         ->setNewValue($pri);
       $xactions[] = id(new ManiphestTransaction())
-        ->setTransactionType(ManiphestTransaction::TYPE_SUBPRIORITY)
+        ->setTransactionType(
+          ManiphestTaskSubpriorityTransaction::TRANSACTIONTYPE)
         ->setNewValue($sub);
     }