Add access restrictions to courses

Access restrictions are a useful tool that can be applied to every activity and resource within a course. It would be additionally useful to be able to apply them to the course itself.

My use case is for when a course has multiple groups with different needs, and one of these needs may be to have a course hidden for a period of time. While this can be achieved by suspending enrolments of individual students, this is time consuming for a teacher to do.

It would also be helpful to automate the enforcement of pre-requisite relationships between courses.