Fix VdfnGraph edge creation / connection building

This fixes wrong output of connection information from VdfnGraph in case one outport is connected to multiple inports from another target node. Due to pointer sharing between inport and outport, the VdfnPort pointer is no longer a unique ID for the ports. Hence the VdfnGraph::GetInportName( ) (retrieve name by pointer given pointer) was removed (it cannot be implemented) and the internal edge map now also registers the string name along with the pointer for reference. This has no effect on the graph traversal, as one edge between nodes is enough to determine the evaluation order. But it is important for clients that want to traverse the VdfnGraph structure, for example to visualize it.

Also, this fix contains enhanced documentation and clarifications and renaming of methods.

CHG: renamed private graph API to clarify its purpose FIX: fixed logger node (remove dependency on deprecated graph API) FIX: fixed persistence to use port name from connection info, not by retrieval