rebooking validations uniqueness on dead appointment and new appointment, as well as presence of both
add re_bookable to rails_admin appointments and todays_appointments views, with help tips
rails_admin initializer new and edit except Rebooking
rails admin config for rebooking
remove TODO comment about auto creating a new appointment when old one is cancelled/rescheduled, called in #create_rebooking_and_new_appointment in after update