- Moves create_default_prior to the core prior file
- Makes fill_prior a class attribute
- Makes the BBH default priors its own file which is read in when
  figuring out the defaults
- Checks the example all still run

Updates so that it no longer uses the PowerLaw (which leaves a confusing
alpha attribute.

added the possibility to change the color scheme of corner plots with the 'lionize' keyword argument

Previously I was setting the noise_log_likelihood to nan in a confusing
way. This removes that and also renames all the liklihoods for clarity.

- Adds a check if the type is correct
- Adds the write to file function as a method

Project restructuring

See merge request Monash/tupak!55

# Conflicts:
#   examples/open_data_examples/GW150914.py