Skip shipments in FreeShipping PromomtionAction if promotion action has already been applied
Work with in-memory objects in PromotionAction::FreeShipping spec
OrderInventory#verify now no-ops if no shipment is determined
Remove test for LineItem that was testing taxes

This is tested thoroughly enough within TaxRate and OrderContents tests
Refactor Promotion::Actions::CreateItemAdjustments to work with in-memory objects

This also included a small reshuffle of the logic for product_ids, excluding line items BEFORE create_adjustment gets called, rather than during