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/DragController.java

@@ -18,16 +18,17 @@ package com.android.launcher2;
 
 import android.content.Context;
 import android.graphics.Bitmap;
+import android.graphics.Canvas;
 import android.graphics.Rect;
 import android.graphics.RectF;
-import android.os.IBinder;
 import android.os.Handler;
+import android.os.IBinder;
 import android.os.Vibrator;
 import android.util.DisplayMetrics;
 import android.util.Log;
-import android.view.View;
 import android.view.KeyEvent;
 import android.view.MotionEvent;
+import android.view.View;
 import android.view.WindowManager;
 import android.view.inputmethod.InputMethodManager;
 
@@ -568,6 +569,9 @@ public class DragController {
         final int count = dropTargets.size();
         for (int i=count-1; i>=0; i--) {
             DropTarget target = dropTargets.get(i);
+            if (!target.isDropEnabled())
+                continue;
+
             target.getHitRect(r);
 
             // Convert the hit rect to screen coordinates