Added the ability to combine orders into a follow-up order via API

Method added to API V8 MarkOrderAsAdditional , which allows you to assign order current follow-up order to order parent. Property GroupOrderId order current is set equal to the property Id order parent, or equal to null if parent == null.

Order current cannot be null, parent can be null if you need to cancel the merging of orders into an additional order. The current order must be open, parent can be an open or closed order. Both current and parent orders cannot be delivery orders.