Yapstone gateway

 New gateway for Yapstone
www.yapstone.com
It's a unique identifier (string) for the property you're booking. I don't think it should be passed as an `initialize` credential, since a merchant can have many properties. It is however, required for most of the transactions (`authorize`, `capture`, `purchase`, `refund`, `void`). You may think of it as the "product" you're buying.

Can you explain how would you pack it into the `authorization`?