Draft: conversion.py script updated

I have added the option to update the waveform_defaults in the functions generate_all_bbh_parameters and generate_all_bns_parameters inside conversion.py, which were hard-coded. This solves the problem when calling the function manually, for example, in the post-processing steps. However, I am not sure how to update those functions which call the aforementioned updated functions while sampling to generate all parameters.