Update unit tests accordingly.  Groups seem to work now.

still producing port mapping bugs...

Update & extend unit tests accordingly.

Further testing needed.

Add unit tests to OpticGraph.
Add unit tests to OpticRef.

Update dependent code accordingly.

Check if all ports in light input data a real input ports of the node to
be analyzed. Otherwise data might be silently discarded. This should not
happen if the nodes are properly connected...

Update examples & tests accordingly.