Merge Co-MFG Purchase Orders

If Purchase Orders (POs) are merged, they lose the link to the Manufacturing Order (MO) that created them.  We'd appreciate this link being kept after a merger.

As an example, we send Parts to get painted.  It is ~20 unique parts.  Ideally, we could merge the 20 POs (automatically generated from their MOs) into one.  Dealing with one PO and Invoice is much easier than dealing with 20.