Also adds thetas_at_ref data to the Writer object

Now forces use of dtglitch = None for no glitches

1) Adds 'add_noise' option (defaults to true)
2) Better checking of Writer for if all glitch parameters have the same
length (avoid strange errors)
3) Fixes issue in which the tqdm ignore command was itself ignored

Transforms the single pyfstat.py into a python module splitting the
relevant code into separate sub-files in pyfstat. This should result in
improved readability.