Legacy payment updates

This loads old payments by merchant_order_id if an order payment can't be found.
Old payment methods are stored in capitals, so change them to lower to look up fee.
Changing the state should save the record (save=True):

@transition(field=status, save=True, source=[StatusDefinition.LOCKED, StatusDefinition.PENDING, StatusDefinition.SUCCESS], target=StatusDefinition.FAILED)
    def failed(self):