Improve the handling of the drop target marker when dragging items within the

grid. Originally the borders disappeared not they don't. A single element is
used to contain the drop target marker. This element contains all the position
information for the drop handler to determine where the item should be
positioned.

In addition, the drop target marker is removed when the drag extends outside
the grid and is re shown, when the cursor re-enters the thumbnail grid.

modules/organize/css/organize_theme.css

@@ -6,6 +6,11 @@
 }
 
 #g-organize-microthumb-grid,
+#g-organize-drop-target-marker,
 .g-organize-album-text:hover {
   border-color: #79B7E7;
 }
+
+#g-organize-drop-target-marker {
+ background-color: #79B7E7;
+}