Support for international bill addresses

For international addresses, the state will be in state_name, rather than at
state.abbr. This allows for payments to be created with such an address.
It looks like there's an [Address#state_text](https://github.com/bonobos/spree/blob/2c71df3/core/app/models/spree/address.rb#L41-L43) method, would that be any better?