addOrderShipmentToShipment should return shipmentItemSeqId

[Forrest Rae]

Hey Everyone,

Am I crazy, or should the addOrderShipmentToShipment service return
shipmentItemSeqId?  It's the only argument that is optional, yet it's a
primary key in OrderShipment.  It's an optional argument to the service,
in case of an update operation.

I created an issue and a patch:
https://issues.apache.org/jira/browse/OFBIZ-5950

-Forrest