Save payment and refund block hashes associated with each enqueued media

[gbl08ma]

To make it easier to understand whether a payment address with a leftover balance should be refunded or not, we should save the payment block hashes with every enqueued media. We can't associate with the played media entity because entries can be removed before they play. We'll likely need a separate database entity for this, which can track the payment transactions and the refund transaction when applicable.