Get rid of useless white space in the code

[kordejong]

The model code is littered with useless white space. Editors that are configured to show white space, like mine, make it hard to read the code. See also the first item here: https://peps.python.org/pep-0008/#other-recommendations

Suggestion: use a pre-commit hook to prevent spurious space to end up in the repository. Something like Black will automatically remove the all useless white space.