Associate new exchange order with same store as original order

When an expedited exchange is not returned, we create a new order so that we
can charge the customer for the unreturned item. That order doesn't currently
have a store associated to it, wreaking havoc in our process. This makes sure
that it will.

This depends on [bonobos/spree#110](https://github.com/bonobos/spree/pull/110)