DO NOT merge

Hi Matthieu,
I had a few python bindings questions to our expert :-).
can you have a look a the python diff?
You changed many things in the python binding and I am not sure how to solve those issues the correct way:

I get a OpcUa::DateTime objects from C++, do we have a way to transform it a python datetime? Any suggestions? there are many places we should do the convertion..

getting server state in example_client.py returns None instead of an int or a ServerState, what would be the correct way to fix this