Set up CI on GitHub Actions

[lancegoyke]

TODO

• add pre-commit #63
• add and run flake8 #68
• Add Black #65
• add blacken-docs #66
• add and run isort #67
• add flake8-bugbear extension #69
• add and run flake8-no-pep420 #70
• add flake8-breakpoint #71
• Flake8 docstrings #72
• add and run flake8-comprehensions #73
• add and run djhtml, not curlylint #74
• Make sure tests run without errors #77
• CI - add tests #80
• set up GitHub Actions - create django.yml #78
• CI - check for migrations #79

[lancegoyke]

As part of this, we'll want to set up pre-commit with flake8 and Black, then run pytest.