To install:
    1. run `pip intall -r requirements_dev.txt` again
    2. run `pre-commit install`

After that all commits to notebooks will clean the output cells and
other meta data which clutters the diffs.

If pre-commit cleans cells you have to commit again. That leaves you
the option to preview the changes from pre-commit

Update of chapter 5

See merge request !64

Dev organization updates

See merge request !65

adjusting figures

See merge request !62