Make all CSS rules for draggable cards/items independent of container classes

Summary:
Ref T5240. With the new approach, the draggable clones lose their containers, so they don't get affected by rules like `.container .item`.

Put classes on the cards/items and use `.board-item.item` and `.standard-item.item` to apply rules instead.

This didn't turn out //too// gross, and seems relatively OK / not obviously broken.

Test Plan:
  - Dragged cards on a workboard.
  - Dragged items in normal lists (tasks, pinned apps).

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T5240

Differential Revision: https://secure.phabricator.com/D15161

src/applications/project/controller/PhabricatorProjectBoardViewController.php

@@ -288,6 +288,7 @@ final class PhabricatorProjectBoardViewController
         ->setFlush(true)
         ->setAllowEmptyList(true)
         ->addSigil('project-column')
+        ->setItemClass('phui-workcard')
         ->setMetadata(
           array(
             'columnPHID' => $column->getPHID(),