[PyQt] scene and layers

[Christopher M. Nahler]

thx. I have been working with parenting before and i think its great. I 
want to try to implement sizing handles as child objects of a graphics item.

before I found the layers functionality I drew my background rectangle 
as first object and parented all other items as children of that. this 
way when i was implementing reordering of items (toFront, toBack etc) I 
did not have to filter the "background" rectangle in order to avoid 
items getting hidden behind the "background".

but for selection it would still include this rectangle. so i am trying 
to find a way to draw a background not as a graphics item and hoping 
that it will not be included in selection.