Reconcile invoices and credit notes

[barredterra]

#111 introduced Multi-Party reconciliation. However, the following case does not seem to be covered yet:

We issue a Sales Invoice SINV-001 for $100 to Customer A.
We issue a Credit Note SINV-RET-001 for $50 to Customer B (who is a subsidiary of Customer A).
We receive a Bank Transaction for $50 from Customer A, with the description "SINV-001, SINV-RET-001".
We want to reconcile the matched Invoice and Credit Note.

[barredterra]

@marination one of our customers has now run into this case.