* Scene graph R-tree based spatial optimization of picked
IElement-material resolution
* Parallel processing for both resolving the elements to pick and
picking the elements
* Added INode -> IElement map management to ElementPainter to have the
fastest possible means available in picking for getting from scene
graph nodes to their corresponding IElement instances.
gitlab #66
Change-Id: I524da0c2695cdda2eb4f0a1fa318f48ff8fcff24