Instead of setting the name of the namespace to the user's username,
set it to the user's name.

This is more consistent with how we name the routes:
The route-name of a namespace is the human name of the routable. In
the case of a user-namespace, this is the owner's name.

When we change a user's name (both on create and update), we now also
update the namespace-name to the user's name. This will make sure that
if we also correctly update all the nested routes.