controller_logon_done
This controller is used as a jumping stone after a log on from the /logon page.
The p argument is passed from the /logon page.
The controller will notify observers of #logon_ready_page{ request_page = P }} to
see where to redirect next.
The notification is a first, so the first module responding
with something else than undefined will determine the redirect.
If no redirection is returned, and the p argument is empty, then the user
is redirected to the home page /.