Add test for recalculating adjustments on line item save
ShippingMethod#create_adjustment is no longer used
[sample] Remove shipping adjustments

These are now tracked in an attribute on the shipment itself
Ensure that ItemAdjustment tracks tax_total separately from adjustment_total
Create real shipment rather than stubbing implementaiton in order_updater_spec
Move update shipments out to its own method + test it correctly in OrderUpdater
Rename 'line_item_adjustment' factory to 'tax_adjustment'

This correctly refers to its purpose
Remove tax_total method that recalculated tax every time
Ensure that tax_totals are tracked when using OrderUpdater#recalculate_adjustments
Only define event transitions if the state machine contains those states

This fixed a state machine test in order/checkout_spec where by simply defining an event transition from the address state, the state will be present within the state machine. We should not define these events at all if the state is not present.
Work with an actual persisted order in payment_spec

This is because the updating proceedure for an order now requires an order to be persisted, due to the persist_totals method in the updater being called

(Should a payment really update every aspect of an order?)
Stub calls to set_shipments_cost where it is no required
Create a proper adjustment in order_spec test