Drag and drop views that share data

The DndView is a subclass of QDragView, implementing additional functionality. When a drag-and-drop is performed between two such views, setting one's value will update the other's as well. Use the 'value' method to get or set the value of a view. When creating a new instance of the view, you can pass in the 'type' argument, which can be \source, \sink, or \both, defining what will be the role of the view.