Update CI to use flake and / or black

[mnlevy1981]

A recent code review for #423 highlighted an inconsistency in the Python code; we sometimes use ' and other times use ". We need to run our code through some automated formatters as part of every PR.

In feisty we are using pre-commit to automate the format-checking, and then one of the Github actions runs the pre-commit packages on a github VM to verify nothing needs to be changed. I think this is a reasonable workflow, and suggest we adopt something similar here.

[mnlevy1981]

Another related issue is that there is still a lot of python2 code in our repository -- e.g. we don't need to convert strings to u-strings, since that's the default type for python3. And it would be nice to have pylint check more of our python files.