[promo] Removes adjustments only if order is not complete

This should help to fix #1046. Still missing some specs and also removes
adjustments in case its promotion becomes inactive

ps. This is a work in progress. I just wanted to report that currently every time a promotion is removed its adjustments are removed as well, no matter what. Due to this line in ``Promotion::Actions::CreateAdjustment``

    has_many :adjustments, :as => :originator, :dependent => :destroy

Hopefully I'll get this done and resolve #1046 before the weekend.