[Python-modules-team] Bug#927117: third-party issue

[Gordon Ball]

It looks like at some point the (not packaged in debian) module
https://github.com/Jupyter-contrib/jupyter_nbextensions_configurator was
installed and added to the nbextension config.

It's not obvious that this can be related to ipywidgets; it might be
related to the old method of setting the nbextension config in
/etc/jupyter/nbconfig/notebook.json, which might conflict after upgrade
with user-level config?

`jupyter nbextension list` should provide more information.