Fix issues with nbstripout on woody

[AKuederle]

At the moment we have the problem that syncing the entire folder with rsync will copy the .git/config file that contains the nbstripout config, which has hardcoded paths to a python version.

In result the git-repo (or at least git status is broken on woody).

Workaround: run nbstripout --install every time on woody after a sync

Solution: Migrate away from nbstripout to jupytext or wait for nbstripout 0.7.0 release which seems to have an option to set the python path to something generic

[AKuederle]

At the moment I "automated" the workaround by running nbstripout on woody as part of the sync script. Not nice... but it works