Run black on repo and add to pre-commit-config

This is to ensure consistent formatting.

The first commit is the big one, after running black on all the code. The second commit is just some manual fixes for multi-line strings. If you want to review anything, look at the .pre-commit-config.yaml change, and the second commit.

I tried blacken-docs as well, but it has some failures if I enable --rst-literal-blocks, which we need for most of our docstrings. It will require a bit more work to fix the various code blocks (some are Python code, some Python console, and some are just plain text). I suggest that waits for a different MR.

Closes #200 (closed) Related #500 (closed)