Ensure that TensorBoard support is optional (when we try to use it)
but add decent documentation and log messages pointing out that it should be installed
This is part of #130
[A venir] Mise en place de quotas sur nos instances GitLab. Plus d'information sur : https://doc-si.inria.fr/pages/viewpage.action?pageId=129728565
[Coming soon] Quotas installation on our GitLab instances. More information: https://doc-si.inria.fr/pages/viewpage.action?pageId=129728565
but add decent documentation and log messages pointing out that it should be installed
This is part of #130