Link Patient Documents and letters to invoice items such that batch numbers can be reported.

The current patient documents and letters are not integrally linked to a item sale, they are linked to a product. They can be created by this linkage. However latter when referencing the item when need a direct link to the invoice item to ensure consistency when reporting batch number and expiry dates.
To achieve this we need to:-

• Update the act.PatientDocument* archetypes to provide a reference to the invoice item.

• Change the layoutstrategy to hide the node if it is empty

This will then allow the display of batch numbers and expiry dates using

• openvpms:get(., "invoiceItem.source.batch.entity.name")

• openvpms:get(.,"invoiceItem.source.batch.entity.product.activeEndTime")

See http://www.openvpms.org/forum/product-code-or-barcode-report