Billable references

We implement a billing system based on unique reference IDs, with the exception being that the creation of a parent reference is not billable. This applies to parent references created from a bill of lading and to parent references created from a booking number.

To provide an example, a bill of lading that is used to track 10 containers will count as 10 active references only. The parent reference is used as a base to determine how many containers need to be tracked and each child reference will have its own unique reference ID. A booking number used to track 10 containers is counted the same way.