it was made a method for handing named_servers,
but that made things way more complicated and replaced a boolean flag with a callable,
which would behave unexpectedly but without error if a boolean flag was expected.
Spawners have properties for dealing with this now, so use spawners
Restore `user.running` as an alias for `user.spawner.ready`
optionally allow admin users to login to user servers by visiting a special admin-only URL that sets the relevant cookie
- disabled by default
- an 'access server' button is added to the admin panel, which sets the necessary cookie to log in to the user server