title: GoJS Keep Group of Nodes copied via DraggingTool
body: <p>Is there a way of copying Nodes with the <code>DraggingTool</code> including their <code>Part.containingGroup</code>? I know the <code>CommandHandler</code> has a property <code>copiesGroupKey</code>, but I can't find any similar functionality in the <code>DraggingTool</code>.</p>
  
  <p>Maybe even better if there is a way to detect on which group the copied Nodes are being dropped to set the new <code>containingGroup</code>?
  Is there an event to subscribe to when copied Nodes are being dropped?</p>
  
  <p>I also noticed the same problem with the "Swim Lanes" sample here
  <a href="http://gojs.net/latest/samples/swimLanes.html" rel="nofollow noreferrer">http://gojs.net/latest/samples/swimLanes.html</a>
  Copying Nodes via the <code>CommandHandler</code> works fine, but if you "Control-Drag" them they are placed outside of any Group which should not be possible at all with that example I guess?!</p>