chore(draggable): jQuery adapter returns Draggable instance

Draggable instance instead of a jQuery collection.
Why? Becomes a mess if Draggable is instantiated multiple times from
the same HTML element.

BREAKING CHANGES: If you was accessing to Draggable instances through
.data('drag') you should remove the `data` getter. Since now the instance
is returned directly.

src/jquery.draggable.js

@@ -358,11 +358,7 @@
 
     //jQuery adapter
     $.fn.drag = function ( options ) {
-        return this.each(function () {
-            if (!$.data(this, 'drag')) {
-                $.data(this, 'drag', new Draggable( this, options ));
-            }
-        });
+        return new Draggable(this, options);
     };
 
 

src/jquery.gridster.js

@@ -682,7 +682,7 @@
             }, 60)
           });
 
-        this.drag_api = this.$el.drag(draggable_options).data('drag');
+        this.drag_api = this.$el.drag(draggable_options);
         return this;
     };