[AdminUI/Order/Refunds] Original payment method detection is incorrect

[diimpp]

In case when there are multiple payment attempts in different states and possibly with different payment methods

RefundPlugin/src/Resources/views/_paymentMethod.html.twig

Line 2 in 02d9399

{% set original_payment_method = order.payments.first().method %}

then this code doesn't work as intended and should be replaced with

{% set original_payment_method = order.lastPayment(constant('Sylius\\Component\\Core\\Model\\PaymentInterface::STATE_COMPLETED')).method %}

as something not outright broken.

Ideally it should be done as new provider and twig function, which can accommodate partial states as well.

[GSadee]

Fixed by #316