[backend] PaymentsController#load_order should return order object, not result of authorize! call
Fix back end payment methods not showing up

Fixes #3233
Add dependent: :destroy to Spree::Shipment.shipping_rates

When an order transitions back from delivery, to a prior state, then back into delivery, shipments are destroyed, but not shipping_rates, leaving orphaned records behind.

Fixes #3349
Merge git://github.com/spree/spree