Adding support for drag and drop of folders and shortcuts. 

also:
- Long press on empty space on workspace now brings up customization tray
- Fixed: while dragging, items appeared to be dropping on folders two cells to the right
- Fixed: Disabling drops on folders when the workspace is shrunken
- Fixed: account for scaling of dragged items when checking if they overlap
          with shrunken workspace screens
- Making folder icons dimmable to match shortcuts and widgets
- When deciding with shrunken workspace screen we're dragging to, we now use the closest screen rather than the one that has been overlapped the most
- Refactored drag/add mechanism, removing array of occupied cells from CellInfo
- Removed dead code/variables
diff --git a/src/com/android/launcher2/DropTarget.java b/src/com/android/launcher2/DropTarget.java
index d2e3ace..308dbbe 100644
--- a/src/com/android/launcher2/DropTarget.java
+++ b/src/com/android/launcher2/DropTarget.java
@@ -23,6 +23,12 @@
  *
  */
 public interface DropTarget {
+    /**
+     * Used to temporarily disable certain drop targets
+     *
+     * @return boolean specifying whether this drop target is currently enabled
+     */
+    boolean isDropEnabled();
 
     /**
      * Handle an object being dropped on the DropTarget