Fix order / adjustment presence in adjustments

* Fix admin action producing adjustments without direct order reference.
* Add validation for the presence of adjustable
* Adjustments without an adjustable item do not make too much sense
* Add migration to fix old adjustments without direct order reference

fixes #5556

Conflicts:
	core/app/models/spree/promotion/actions/create_item_adjustments.rb
	core/spec/models/spree/adjustment_spec.rb
	core/spec/models/spree/calculator/refunds/default_refund_amount_spec.rb