Join a Carpool: Multiple Reservations

[erin-king]

As a user,
when I join a carpool,
I have the option to reserve more than one seat and no more than the total number of available seats.
When I view the carpool, I will see my name listed once (ex. "Erin K") and I will see for my additional passenger "'s Guest" (ex. "Erin K's Guest)