Added rates and pop stuff
Adding rates and pop codes for computing injection distributions found here to gstlal-ugly. Three files (lvc_rates_injection_dag, lvc_rates_injections, lvc_rates_plot_injections) are added to gstlal-ugly/bin, and three files (cosmology_utils.py, injection_generation_dag.py, injection_utils.py) are added to gstlal-ugly/python