Add linting for python code

[xylar]

New linting for all file types includes:

• checking for trailing whitespace
• checking for correct end-of-file

New linting for python code includes:

• sorting imports
• using f-strings to format strings
• following PEP8 code style (with flake8)
• variable type checking with mypy

The conf.py file in the doc directory has been linted using these new tools.

Documentation has been added on linting.

Issues with trailing whitespace and incorrect end-of-file formatting have been fixed in many, many files.

Checklist

• Documentation:
  • Developer's Guide has been updated
  • Documentation has been built locally and changes look as expected

[philipwjones]

Looks good, thanks for adding this @xylar Clearly needed based on all the changes as a resulting of linting.

[xylar]

Thanks @philipwjones. I'd like to turn on the remaining C++ linting but it seems to want to actually build the code with cmake, which is a lot more complicated than I realized that workflow was going to be. Perhaps we can chat about that at some point soon, but I'll first need to take some time to even see if I can get it working on some machine or other.