Add auto-deletion functionality into LayoutAnimator which can be used to delete the item when its removal animation finishes. Emit a signal when the state of an item in the animator changes. Avoid repeatedly setting an item's geometry with the NoEffect effect.

Added a DeadState into which items transition after their removal animation finishes or if they have not been added to the animator. When inserting an item with a fade in effect set the opacity to 0 if the item is a widget.