Enrollment Rules do not handle nested groups

[battis]

Same as this issue in the global navigation menus and with the same reason: I should just be using an RBAC library, like a big boy.

┆Issue is synchronized with this Asana task

[battis]

Seems like moving towards a more object-oriented way of working with groups would allow for sharing code across repositories, solving multiple problems at once and abstracting away this problem.

In fact, moving all of Custom Prefs into an object-oriented structure solves a lot of abstraction woes…