Enable GitHub Actions CI

[stefanor]

Some CI to keep tests passing.

Had to unpin versions in requirements.txt for them to be installable. You may want to have a separate test-requirements, or just script the unpinning in the test job.

[reilleya]

Looks good! One comment but otherwise I think this is ready to merge. I hadn't realized that github has built in CI.

This is another case of something that I should have documented, but there is a pylintrc file checked in that we should have this use if switching it isn't too difficult. If I remember correctly, much of the UI code raises low level warnings while the simulation code is pretty clean.

[stefanor]

I had a look, but can't see an obvious way to do anything useful with pylint.

Pylint gives very granular feedback, so you don't want to use it as a pass/fail check, you rather want something to comment on every line of the MR that generates feedback. I think github actions can do that. But I haven't dug in at that level, and I'm not going to for a drive by PR :)

So, probably simple enough to swap that (stock template) flake8 with a pass/fail pylint. But more than that is more complex.

[reilleya]

Makes sense. I'll into using pylint in the future but this seems good for now.

Thanks!