warn when adding existing node or labeled edge
warn when adding existing node or labeled edge

The warning is logged for node, not visible to the user.
This will enable merging States with LabeledStates and replacing:

- LabeledStates.label -> States.add -w-> LabeledDiGraph.add_node
- LabeledStates.labels -> States.add_from -w-> LabeledDiGraph.add_nodes_from
- LabeledStates.label_of -> States[state] -w-> LabeledDiGraph.node[state]

and merging Transitions with LabeledTransitions and replacing:

- LabeledTransitions.add_labeled -> Transitions.add -w-> LabeledDiGraph.add_edge
- LabeledTransitions.add_labeled_from -> Transitions.add_from -w-> LabeledDiGraph.add_edges_from
- LabeledTransitions.remove_labeled -> Transitions.remove

where -w-> stands for "wraps", and remove:

- LabeledStates.label, .labels, .label_of
- LabeledTransitions.label, .relabel, .add_labeled, .add_labeled_from

tulip-control/tulip-control,necozay/tulip-control,tulip-control/tulip-control,tulip-control/tulip-control,necozay/tulip-control,necozay/tulip-control,necozay/tulip-control,tulip-control/tulip-control,necozay/tulip-control