Maint/isort

[mschmidt87]

This PR introduces isort to our tools ensuring common coding standards and uniform layout across the library.

isort sorts import statements in a particular, reproducible order, namely like this: FUTURE,STDLIB,THIRDPARTY,FIRSTPARTY,LOCALFOLDER

This PR:

• applies isort to all files in the library, testsuite, and examples. Therefore there are a lot of changes in many files, but they are just about formatting, mostly to the imports. Some changes are introduced by black as well (trailing commas in function definitions). I am not sure why this happens.
• adds a config file for isort
• adds isort to the required dev libraries
• adds isort as an additional check to the CI.
• adds my pre-commit configuration file to the repository. This will make it easier for other contributors to install the pre-commit hooks using that config file.

[jakobj]

so.much.tooling 🤤 🚀

thanks, this looks great! this has always bothered me, nice to see it's so easy to solve. added two meta comments.

[jakobj]

looks good, thanks! 👍

[jakobj]

before we merge, please squash the commits

[mschmidt87]

Thanks, I organized this now into 5 commits, which makes sense, in my opinion. Objections, @jakobj ?

[jakobj]

i'm happy! merging :)