Fixed a bug where close buttons were removed
Delivery animated if either bird or nest visible
Ensures that children have higher z-index

Since drag was sometimes dragging the whole widget backside rather than
a widget on the back.
Bird copies start where bird is

Even when nested deep in a box on the backside of a widget.
z-ordering improved
Parent updated when removed from backside
Another z-ordering fix
Can reset parent

Setting parent to undefined was broken.
Another z-index fix

This ensures that descendants beyond children are in the correct
z-ordering.
Delivery if either a bird or a nest copy is visible

An animated delivery is created whenever either end is visible.