Don't trigger exception if payment processor ID not found for IPN, use debug function because we don't have access to getPaymentProcessorLabel() function

Refactor Mjwpayment.get_contribution so it accepts order_reference and trxn_id params and returns a single contribution with matching payments

Use Mjwpayment.create_payment instead of Payment.create API in updateContributionRefund() for compatibility with multiple versions of CiviCRM