Show reconciliation lines on paid invoice
We show the payment lines on the invoice when it is not yet paid. But once the invoice is paid, there is no information about the lines paying it.
I propose to add a function field which shows the lines linked to the reconciliations paying the invoice.
We should not use the payment lines because it is not always filled (e.g. if reconciliation is done with the wizard and not the statement). Also it would be wrong to fill the payment lines with the reconciliation lines because:
* it could add other invoice lines which are reconciled together.
* it duplicates the information which is already stored on the reconciliation
* we will lost the payment history encoded by the user if the invoice is unreconciled.