Improve minor workboard drag behaviors

Summary:
Ref T5240.

  - Add proper class when dropping cards.
  - Add proper class when creating new cards.
  - Make X-drag explicit so that it works if there's only one column.
  - Stop tootips when dragging, resume them after dropping.
  - Move CSS rule for consistency.
  - Allow user to hit "Escape" to cancel an in-progress drag.

Test Plan:
  - Dropped cards.
  - Created new cards.
  - X-dragged on a workboard with one column and a dashboard.
  - Dragged over a tooltip (no tip), dropped, moused over tooltip (tip).
  - Hit escape during a drag.

Reviewers: chad

Reviewed By: chad

Subscribers: cspeckmim

Maniphest Tasks: T5240

Differential Revision: https://secure.phabricator.com/D15163

src/applications/project/controller/PhabricatorProjectMoveController.php

@@ -160,6 +160,8 @@ final class PhabricatorProjectMoveController
       ->setProject($project)
       ->getItem();
 
+    $card->addClass('phui-workcard');
+
     return id(new AphrontAjaxResponse())->setContent(
       array('task' => $card));
  }