Refactor Promotion.applied scope to query faster

* Before the scope did two joins. Joining the join table and than the
  orders table. As joining the join table is sufficient to define the
  result set removing one layer of joins significantly speeds up the
  operation on large order tables.

Fixes #5453
Assign store id to each order.
Associate new exchange orders with the same store as the original order

Replaces #110.

Fixes #5440
Remove check thats no longer necessary.