Sets or gets the drop target. The drop target is a DOM element(s) for which jqxDragDrop triggers events when the user drags or drops the draggable element over that element(s). The drop target can be specified by using a selector or an object. If the user drags the draggable element over the drop target, the onDropTargetEnter event will be raised. If the draggable element is inside the drop target and the user drags the element outside the drop target, the onDropTargetLeave event is raised. When the user drops the draggable element over a drop target, the onTargetDrop event is raised.