Implementing remaining PKPaymentAuthorizationViewControllerDelegate methods

I haven't written any tests since this is basically just a passthrough of the delegate calls. We found it useful since we're calculating tax when a user selects an address on the Apple Pay sheet.

Not sure if defining methods in `BTPaymentMethodCreationDelegate.h` as `@optional` is the best way to go. Any suggestions?
:+1: @mickeyreiss. I like the idea of offering a `PKPaymentAuthorizationViewControllerDelegate` property.