- [x] Send different email when user is placed on the waitlist, than when is added to attendees. (`attendEvent` mutation)
- [x] Don't add user to the calendar event, if user is placed on the waitlist. (`attendEvent`)
- [x] ~~Move user from the waitlist~~, if attendance of another user is deleted. Send email about being off the waitlist. (`deleteAttendee`)
- [x] ~~Add user to the calendar event~~, when moved from the waitlist to attendees, in case of another user cancelling attendance. Send email about being off the waitlist. (`cancelAttendance`)
Few tasks related to events at full capacity.