Restore the "execute" button of TryWhy3 (fix #541).
This commit also improves the messages displayed to the user.
Prochaines maintenances programmées: lundi 06/05, lundi 03/06, lundi 01/07
Pour plus d'informations: https://doc-si.inria.fr/display/SU/Gitlab
This commit also improves the messages displayed to the user.