Email notifications for admins / instructors:
Send admin an email when a class is booked by a participant
Send admin an email when an event is registered by a participant
Send admin an email when a pass is bought by a participant
Send admin an email when a membership is bought by a participant
Send admin an email when a membership is cancelled
Send admin an email when a membership payment fails
Send admin an email event start reminder
Send admin an email class start reminder
