each form for the appointment in appointments index is remote true
TODO appointment#book(user_id)
user#can_book?(appointment_id) validates that the appointment is persist-able
user#can_book?(appointment_id) immediately returns false if appointment has a user
small work in charges_controller #create, still needs work
appointments_controller#update verifies that the user can book the appointment before moving on to next step, if not shows error modal. error modal needs work
new modal in appointments that states that an overlap exists
buggy js to reload parent page when modal closes