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/FolderIcon.java

@@ -29,7 +29,7 @@ import com.android.launcher.R;
 /**
  * An icon that can appear on in the workspace representing an {@link UserFolder}.
  */
-public class FolderIcon extends BubbleTextView implements DropTarget {
+public class FolderIcon extends DimmableBubbleTextView implements DropTarget {
     private UserFolderInfo mInfo;
     private Launcher mLauncher;
     private Drawable mCloseIcon;
@@ -43,6 +43,10 @@ public class FolderIcon extends BubbleTextView implements DropTarget {
         super(context);
     }
 
+    public boolean isDropEnabled() {
+        return !((Workspace)getParent().getParent()).isSmall();
+    }
+
     static FolderIcon fromXml(int resId, Launcher launcher, ViewGroup group,
             UserFolderInfo folderInfo) {