Deleting a public or private space, what happens to their resources? #2

This was tested in hep-training/TeSS#3 (comment) and we should add something about this in the user docs.

Deleting private space: documentation -> Deleting a private space, deletes private materials (as a non authorized user, it went from a Not authorized to 404; as admin you cannot see space nor materials in /Materials and using the URL) HOWEVER private space URL is still running (which is normal as the route is not deleted) but shows the default UI. -> to add in documentation: "Deleting a private space deletes the resources linked to the space, but the administrator must erase the route associated to the space to avoid users to still visit the private space URL (which shows the default space)."

Deleting public space: documentation -> Deleting a public space, moves material in the default space, thus shows it to any user.