- Moves the hyperPE likelihood to core
- Adds the GaussianLikelihood
- Update docs
- Update examples

- 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

Implemented parameters and non_standard_sampling_parameter_keys as properties that refer to the respective attribute of the waveform generator. This will ensure consistency between the parameter list of the waveform_generator and the likelihood.

and time marg before moving onto dist and tiem nad phase marg

ratio looks a bit off: need to figuring out what's going on with the
normalization

table for distances

Moritz Huebner: Added check if the prior has been set to None. Will set it to an empty dict in that case.

- Added parameters attribute to the base class
- and added calls to the base class in the subclasses.
- Also fixed some typos

This reverts commit 3860e42d. Which I
mistakenly removed.