Support drag-and-drop to set cover images on workboard cards

Summary: This was slightly more complex than I believed, but not too terrible.

Test Plan:
{F1096126}

  - Also used some normal file uploaders to make sure I didn't break that.

Reviewers: chad

Reviewed By: chad

Differential Revision: https://secure.phabricator.com/D15202

src/applications/project/controller/PhabricatorProjectBoardViewController.php

@@ -219,6 +219,9 @@ final class PhabricatorProjectBoardViewController
       'projectPHID' => $project->getPHID(),
       'moveURI' => $this->getApplicationURI('move/'.$project->getID().'/'),
       'createURI' => $this->getCreateURI(),
+      'uploadURI' => '/file/dropupload/',
+      'coverURI' => $this->getApplicationURI('cover/'),
+      'chunkThreshold' => PhabricatorFileStorageEngine::getChunkThreshold(),
       'order' => $this->sortKey,
     );
     $this->initBehavior(