Allow changes to reservation on Create Reservation page

[mnquintana]

Currently, if there's a problem with the reservation (ie. something fails a validation), for the user to fix it, they have to go back into the cart, make their changes, click Make Reservation again, and hope nothing fails. Patrons should be able to update their cart reservation on this page, preferably inline with AJAX, to improve the user experience.

[orenyk]

This is a great idea. In addition, we should definitely emphasize the user name and start / end dates so that it's easy to tell if there were any issues with the cart update (see #522).

[orenyk]

bumping this to 4.0.0

[orenyk]

bumping to v4.1