Update Admin UI for multiple reimbursements per customer return

Tweaks the admin ui a bit so that multiple reimbursements per customer return are displayed
correctly.

We originally only expected a single reimbursement per customer return. But with expedited exchanges
there may be a reimbursement that happens immediately (the exchange shipment) for any exchange items
and another that happens later when the return items arrive and the other non-exchange items are
reimbursed.  This new display logic is more robust in any case.