With the core "purchase" module, in a purchase order a button "In Shipments" lets the user see the picking that was generated by the order itself.

With this module, that button is replaced by an "All Shipments" button that shows the original picking, and all others that are grouped with it. This should include pickings associated to the procurements that generated the purchase, and also pickings that have been chained with push rules.

This is consistent with the "sale" module, where from the sale order the user can access the generated delivery and all chained ones.

The implementation uses the procurement group of the moves in the generated picking. The procurement group is always present in purchases, also when there is no procurement.
