Select cart or target line items by custom type key

It is now possible to define Cart Discounts by specifying the custom Type of the line items to be discounted or the line items that activate the discount.

• [API] Added custom.type.key and custom.type.id Cart Predicate supported in
  • the LineItemPredicate to specify which line item a discount is applied to.
  • and CustomLinteItemPredicate to specify which custom line item a discount is applied to.