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/LauncherModel.java

@@ -1478,11 +1478,11 @@ public class LauncherModel extends BroadcastReceiver {
     }
 
     ShortcutInfo addShortcut(Context context, Intent data,
-            CellLayout.CellInfo cellInfo, boolean notify) {
+            int screen, int cellX, int cellY, boolean notify) {
 
         final ShortcutInfo info = infoFromShortcutIntent(context, data);
         addItemToDatabase(context, info, LauncherSettings.Favorites.CONTAINER_DESKTOP,
-                cellInfo.screen, cellInfo.cellX, cellInfo.cellY, notify);
+                screen, cellX, cellY, notify);
 
         return info;
     }