title: google wallet api: specifying sku?
body: <p>in the google wallet merchant center, if I click on one purchase I am taken to detailed panel where an "SKU" field is displayed along with item name and description.<br>
  While name and description are filled just as they were specified during the purchase (in the jwt), the SKU (aka item id) field is empty. 
  not surprisingly since it wasn't specified in the jwt.<br>
  not surprisingly since there is no place for it in the jwt specs.<br>
  so why is the field present in the order details in the merchant center?<br>
  is there any way to get the SKU to be present during the purchase?</p>