PEP8 fixing and general linting

[organisciak]

@bmschmidt: I rebased all my commits into one squashed commit, so that it doesn't clog up the BW commit history. I still have the original 9 commits locally if you prefer that.

This is the more important or less drastic fixes moving toward https://github.com/Bookworm-project/BookwormDB/issues/98. The remaining issues I think we can tackle incidentally during other work rather than a big 'pulling the band-aid' correction. I mainly wanted to get the codebase to a place where it's easier to spot potential bugs by sight. This process already helped find some breaking bugs, like three references to variables that aren't set.

Below is the commit message for this pull request.

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Adding some errors to ignore list, and fixing the following warnings/errors

• F401: unused imports
• F812: list comprehension potentially redefining out-of-scope variable
• F841: undefined variables called
• F811: double imports
• E70*: Multiple statements per line and ending semicolons
• E10* and E50*: Indentation and backslash style issues
• E221, E222, E241: Unexpected multiple spaces
• E201, E203: More unexpected whitespace

[bmschmidt]

Thanks so much for taking this on: it's very helpful. And your changes in setup.py have instructed my emacs to let me know when I'm not following the styleguide, so I can participate in the slow addition and deletion of spaces going forward.