*on the hub registration form, if revert the hub settings from global to not publish or not global => following the selected settings:
- delete the hub reference into the hub directory
- remove the associated courses associated to this hub (however if a course if referenced also by another hub , the course DB entry is not deleted, just updated)
*on the site registration form on hub (other than Moodle.org), display hubs where the site is already registered. Next to them a button the unregister. When clicked, remove the site and courses information from the hub.