Add black to CI

[markus-hinsche]

I saw that it is written 127 chars in the flake8 part of CI.yml.

I use 120 chars in all related projects, maybe we can agree on this

[markus-hinsche]

@kbressem

I saw that it is written 127 chars in the flake8 part of CI.yml.

I use 120 chars in all related projects, maybe we can agree on this

[markus-hinsche]

Are you sure this won't interfere with isort?

Yes, I am pretty confident, because black only changes whitespace, but not the ordering of chars/lines