Handle orders paid with customer's balance more gracefully

[frankie567]

If a subscription is downgraded (e.g. $100 plan to $10 plan), Stripe will set the overpaid amount to the customer's balance and use it to pay subsequent invoices until it's exhausted.

We handle that properly on our side in the sense that we correctly create an Order with the invoice amount and don't create balances on the Account's ledger.

However, we might be a bit more explicit about it in the order details. I would suggest to:

• Record and show the actual amount paid, so it reflects if the Order was paid using remaining balance
• Hide/disable refund button for those orders since they don't have a payment associated

I believe it'll become even more common once we ship #4777.