Remove hourly from the default policy, add monthly (retain 12) and make all copies at 21:00.
Set the empty string as default value for Client::url so that it doesn't complain if you try to create a client with an empty url.
Avoid a redirection error when the creation of a client fails. Show 404 if you try to edit a client which doesn't exist.
Remove the rather arbitrary upper limits to the count spinners.