Remove PerItem calculators for CreateAdjustments promotion action

These are now taken care of with the CreateItemAdjustments calculator instead
Rename activator_id column in promotions rules and actions table to promotion_id
If there are no applicable rules, then Promotion#rules_are_eligible? should return true, not false
Show line item adjustments only underneath item total in checkout/summary
Only show line item adjustments in cart view

Tax adjustments are displayed on their own, and shipping total is included at the bottom.
Iterate through groups of inventory units rather than each inventory unit one at a time in Shipment#to_package

Imagine in the case where there are 100 inventory units for the shipment. In this situation, the old code was calling this code 100 times:

package.add inventory_unit.line_item, 1, inventory_unit.state_name