Remove duplicated order dir under core spec/models
Recalculate taxes after promo adjustments applied

Introduce three new methods to OrderUpdater (update_promo_adjustments,
update_shipping_adjustments, update_tax_adjustments) and make the order
tax an open adjustment so it can be recalculated after a promotion is
applied.

This should make taxes value more accurate when promo discounts are
applied on the order level