signed_networks: link_prediction: link.py: converted to a generic edge_proportion_over_time function
signed_networks: link_prediction: link.py:  edge_sign_change_and_total_edges function written
signed_networks: link_prediction: link.py: all curves in single plot
signed_networks: link_prediction: link.py: updated axis labels
signed_networks: link_prediction: link.py: wrote test and fixed bug
signed_networks: link_prediction: link.py: template for number_of_hops_before_forming_edge written