much faster than calculating distance distance

It is still very slow, I will try to improve performance

The results are now directly flushed to the disc so, if a simulation is taking too long, we can stop it and restart where we are

It allow the simulator to run multiple simulation at once (but not yet multiple runs)
and to let the system decide how it should scale on each computer

You can now run a lot af simulation and save the results in a .csv file

Betweeness centrality has been removed : it was making things much slower and wasn't needed right now. We will enable it when we need it
main.ccp has been split into 3 files :
    graph.cpp for graph generation and manipulation
    results.cpp to gather the results of the simulation
    main.cpp to launch the simulation and display the results

Adding propagation.py, not functionnal yet

Conflicts:
	main.py

    The connections who had failed are now removed correctly from connection_dict