First attempt to intergrate the relationship graph into sketchup.
Ideally I would like to have a callback if any of the referenced sketchup entities changed in the model space, that will then allow me to re-evaluate the containers that depend on this node. That would mean obersevers in sketchup API term. However, from what I tried and read in various forums, not all oberservers gives the desired results. So after some testing I arrived at something that works in the model space. How it works in components and groups is yet to be tested.