Clean role-less nodes from the node graph

[tobami]

A possible reason that the node graph breaks under some situations is that there are nodes that have no role assigned and are added to the top-level graph instead of a cluster. An option would be to just not add them at all, another to create a "norole" cluster.

[tobami]

Another option is to add a cluster with the recipe name. If the node does not have either roles nor recipes assigned, don't display it at all.