Add pre-commit config and apply changes (#54)

- Add .pre-commit-config.yaml with initial config.
- Add python black pre-commit config
- Apply pre-commit code changes
- Add information to CONTRIBUTING.md
- Add pre-commit to build requirements
- Run pre-commit during travis CI build
- Use a travis build matrix to control when pre-commit runs
  in the CI process. Use explicit include to only run
  pre-commit on Python 3.9.

TODO.md

@@ -7,4 +7,4 @@
 * [ ] Add CI test for Docker image
 * [ ] Add CI to push server to Docker hub
 * [ ] Support common badge server URL structure
-* [ ] Documentation for all docker bits
+* [ ] Documentation for all docker bits