[Cuis] DragAndDropAreaMorph and PartsBinMorph

[H. Hirzel]

Hello Juan

You recently added a
    DragAndDropAreaMorph

which serves very well as an example of a morph with only 7 methods
added which does a lot. It helps to see what is needed to override.

A follow up question: How do I implement a PartsBinMorph?

This means a container which has other morphs inside which I can drag
out and get copies of them.

Kind regards
Hannes