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

src/com/android/launcher2/PagedView.java

@@ -334,7 +334,7 @@ public abstract class PagedView extends ViewGroup {
     }
 
     @Override
-    protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
+    public void onLayout(boolean changed, int left, int top, int right, int bottom) {
         if (mFirstLayout && mCurrentPage >= 0 && mCurrentPage < getChildCount()) {
             setHorizontalScrollBarEnabled(false);
             int newX = getChildOffset(mCurrentPage) - getRelativeChildOffset(mCurrentPage);