Renamed graph_utilities.py to igraph_utilities.py. Included a class to
handle igraph objects.

Init commit: add_node_degree_to_optdis_results.py for creating textfile
containing node degrees for each optdis result. 

calculate_node_edge_networks.py -> removed extra blank lines at bottom.

plots.py -> Changed graph_utilities to igraph_utilities to accommodate
renamed utility file.