- Also applies Black for future inclusion

?

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

This updates to an anaconda python image and removes redundant tests
rerunning examples so that the tests finish in a more reasonable amount
of time. Many requirements are also moves to an
optional_requirements.txt file.

Previously renamed example not updated in tests

- Adds a tests flag for which the sampler only runs 100 steps
- Set the samples as random samples to test plotting
- Fix problems in a few of the examples