improved ngScroll, Events and ngScroll

Include improvements for the scroll and clone.

• When you add the directive ng-drag-scroll. You can add an attribute
  "scroll-element" which contains a jQlite selector. The elements of this selector are going to scroll when you put the draggable on the borders.
• Now, when being hover a ngDroppable, the ngDragClone also gains the
  class "drag-over"
• Attribute ng-drag-clone-group="groupename" let your specify a group to
  link a specific draggable to a specific ngDragClone
• Now, the ngDragClone automatically copy the html and classes of the
  draggable.
• You can deactivate the copy with the attributes on both, the ngDrag
  and NgDragClone by using the attribute ng-drag-clone-copy-class="false"
  or ng-drag-clone-copy-html="false"
• You can specify which element child of ng-drag-clone is going to contains the html copy by including a html query inside ng-drag-clone-copy-class. Example : ng-drag-clone-copy-class=".element-class"
• Can add class to the clone by the ngDrag with the attribute
  ng-drag-clone-add-class="test"