Linked to issue 26, but with a complete patch.

Not sure what your final plans are. But we are needing to drag items from controls which are not item controls. such as DevExpress Grids, Images etc

At the moment the DragInfo was tightly couple to the Drag Source being ItemsControl.

This patch abstracts the creation of DragInfo behind a factory allowing for other IDragInfo to be created.

Factory can be set like the handler via dependency property