Suite à des améliorations dans Guix

As a consequence auctex, among other things, was not found. I don't
know why but let's avoid relying on default value anyway.

Some polish is still required though but we should talk about it. I
need some feedback.

Random notes/thoughts. Major reorganization to come.

Une correction faite il y a 3 mois qui avait été perdue due
à un "git push" oublié...

Ajout fichier d'install de l'environnement Jupyter pour MacOS. Commande : conda create --name mooc_rr --file osx-64.txt