Initial enrolling
Moar enrolling
event_members

Allows students to belong directly to an event, if needed
Enrolling, f**k yeah
And more enrolling options
Relationship cleanup hook
Test Cases for Enrolling
No lesson_team atm
Allow simple unenrolling from CRC
Merge branch 'feature/enroll' into develop

- Allow direct assignment of members to events, no need for lessons, etc.
- Allow self-enrollment of students, probably secured with a shared password