User Course Specific Roles unregistered users break notifications or do not get notifications
The notifications system relies on the user existing. Whenever notifications are sent to users bound in UserCourseSpecificRoles, it will crash upon creating the notification (because it links to a fake user with id -1). These users should probably just get the email, but no notification should be registered.
This requires that the notification system of Project Forum is changed sufficiently where the notifications shown on site are uncoupled from the actual email sent.
Related to !1003 (merged)