Add Github actions for rtd, tests, build docker, push docker registry, push to PyPi.

[cneskey]

Switch to Github actions:

• readthedocs
• Run tests via github
• Build docker container
• Push docker reg
• Push to PyPi via github
  • https://github.com/Hive-Systems/pyfair/actions
  • https://pypi.org/manage/project/pyfair/settings/publishing/