Allow to remove a view object from parent and move to another parent

[Phillipus]

Should be able to move a diagram object to new parent.

JB suggests:

Maybe we could extend object.add(element, x, y, width, height) so that it accepts also a visual object (and in such case, change its parent).

See https://forum.archimatetool.com/index.php?topic=1327.0