Remove Activator class, rename spree_activators to spree_promotions
Remove deprecated increment_quantity and decrement_quantity methods from LineItem
Check for price adjustments using adjustments.price in tax_rate_spec
Apply 'refund' label correctly on tax rates
Only check for price charge adjustments in tax_rate_spec, not ones that are just refunds
Saving a line item will now only update its adjustments and recalculate the order's total
Define final_amount method for LineItem to get amount + adjustment_total

Used in calculating order's final total
Set line items as inverse of order's line items
Update an order's totals when saving a line item
no need to create a tax charge for an order when it's first created:
Move responsibility for updating totals into update_totals method
Stub amount in calculator/shipping/price_sack_spec
Correct comment in state_machine_spec about TaxRate.adjust
Correct OrderUpdater tests
Correct arguments for creating an adjustment in promotion_spec
Ensure ensure_correct_amount adjustment is called in shipment_spec