WL-168 When redeeming a Registration Code in the shopping cart, the user should be redirect to the Registration Code Redemption page

@chrisndodge @smagoun 

Kindly review the changes for WL-168

Thanks
What happens if there are two items in the cart that are both order items for the same course?  For example, in the future a user may want to purchase a verified certificate as well as access to a private cohort, both for the same course.  Would it make sense for this method to return *all* such items as a list, instead of just the first one it finds?