Transaction details "virtual size" does not account for sigops

[luke-jr]

    strHTML += "<b>" + tr("Transaction virtual size") + ":</b> " + QString::number(GetVirtualTransactionSize(*wtx.tx)) + " bytes<br>";

GetVirtualTransactionSize fails to account for sigops if passed the transaction alone.

This could confuse a user into thinking the transaction they were sent, still unconfirmed, has a reasonable fee rate, when it might very well not due to a bunch of sigops in another output or input.

Annoyingly, GetTransactionSigOpCost looks liable to assert if used on a confirmed transaction. It wouldn't make sense to stop reporting the correct virtual size after a transaction confirms, so this looks like a pain to fix.