added isDraggable back to Node

src/Node.js

@@ -100,6 +100,13 @@
                 });
             }
         },
+        /*
+         * the default isDraggable method returns false.
+         * if the DragAndDrop module is included, this is overwritten
+         */
+        isDraggable: function() {
+            return false;
+        },
         /*
          * when the logic for a cached result depends on descendant propagation, use this
          * method to clear self and ancestor cache