[FIX] stock: issue #3562 - tax and discount not carried over to the extra move

Apparently some fields were missing when creating the extra move object for it to be processed correctly by the invoicing module. This fixes the issue by inheriting links from the original move.

Rel to: #3562 
This is problematic as you are not sure the op has any move related.  This should be conditional.  Moreover, it does not make sense to copy all those values as most will have been attributed to the picking already.  For the procurement, it is even wrong as the extra move is not related to that procurement.  This move is also make to stock.  Moreover this is changed in stock/stock.py where purchase lines don't exist and this might be the main reason for this PR.