When waitlisted class is opened for registration, allow waitlisted students to add themselves to class

We have several classes that are waitlisted pending sufficient numbers of students, and sometimes the students have been on the waitlist for quite some time. We can't assume a student still wants to register for a class in which they are waitlisted.

When the class becomes available to start because there are finally enough on the waitlist, it would be much easier if we could email them to (this is the idea) add themselves to the class if they still want to take the class rather than having to go into Registration Manager to do it.

This way we would know for certain if all those waitlisted students still want to take the class and then start or continue waitlisting the class.