Changes to docstrings. Deleted redundant  mean_quenched_fraction methods.
Fixed Zheng07 so that passed parameter_dict is actually used
Fixed assembias_HOD models so that the passed baseline_HOD_param_dict is actually used
Modified vdB model so that passed baseline_HOD_param_dict is actually used
Polynomial_Assembias_HOD_Quenching_Model now instantiates without bailing