Support proper HST model feedback regarding HST configuration nodes in /console

Currently, there is a poor man's solution in the /console servlet that through the HstReferenceEditor tries to trace references between HST configuration JCR nodes. However, the HstReferenceEditor cannot re-implement and keep in sync the entire HST model. Instead, a different approach is required: With the UUID of the configuration node a call should be done to the HST enhanced model (for example via some rest proxy or in case the model is a service to the service) that returns info about

1) which configuration nodes are using that node (if none, the node can be safely removed for example)
2) whether the references of that node are reachable
3) etc etc