GitLab

This reverts commit d03e7b73.

- Also applies Black for future inclusion

1) Restrict the dynamic dynesty test to maxcalls of 100
2) Split the sampler_test out of the main tests and into a separate
node. This means the sampler_test doesn't contribute to the coverage

`python setup.py install` is not exactly the same, `pip install` validates more of the metadata

This adds a test-mode command like argument to run with zero likelihood.
As such, this will sample from the priors alone. To use, run any
standard bilby example with `--bilby-zero-likelihood-mode` in the
command line. This has been intentionally obfuscated to avoid
overloading the usual documentation.

- Make the test case generate samples from the prior
- Force the marginalized likelihood test to use fixed m1 and m2 to
  ensure no samples are generated with the wrong ordering
- Remove pipenv

to make sure the core dependencies are specified properly

1) Rename all tests to the pytest standard naming convention
2) Update to use pytest to run the tests and collect coverage
3) Simplify gitlab CI script using above changes