CompositeGeometry transform linking

Right now, CompositeGeometry overrides the transform of any Geometry added to it. Not quite sure if that is intended, but it definitely makes CompositeGeometry less useful. 
This pull request fixes this by making the CompositeGeometry transform the parent transform of any added geometry. 
IMPORTANT: If this should be merged, there are a few places where the parent has to be unlinked again when the geometry is removed. Haven't added that yet, but I could later.