Update the mod-order-storage RAML and moduleDescriptor to support implementation of the po_line_number API.
The sequence_number json schema consists of a single field: "sequenceNumber", and would be shared by the /orders/po-number and /orders/po-line-number endpoints... e.g.
- RAML is created/updated for this API
- the sequence_number schema is created (and examples)
- the module descriptor is updated w/ the new endpoint, permissions, etc.