Factorize in same class build nodes and graphs

[marota]

From Grid2opSimulation.py and PypownetSimulation.py you have the same functions for creating nodes and egdes of power flow or distribution graphs. This should be factorized in the same file or class. Could move them in constrainedPath file and rename this file graphsAndPaths ?

[marota]

build_graph_from_data_frame, build_edges_from_df, build_detailed_graph_from_internal_structure could also be factorized ?

[marota]

Create a plot.py file to which to move common plotting functions ? It is not really related to simulation per say, but there are currently expected methods in simulation.py