Remove Activator events
Promotion::Actions::CreateAdjustment now applies adjustments to line items rather than to the whole order
Remove Activator class, rename spree_activators to spree_promotions
Remove price_adjustments method which is now no longer useful
Remove adjustment callback nonsense

We should really do this with a single method call after an order has been updated, rather than getting the order to update each adjustment which triggers the order to update once for every single adjustment applied to the order
No need to call reload any more in update! on adjustment
Promotion code checking is now done in CouponApplicator, so we don't need to duplicate this inside Promotion#activate too
clear_adjustments! is long gone, as is ship_total
Remove Shipment#cost tests, replace with #amount tests