Add QR codes to student invoices when you mass print outstanding invoices.

So I do have to say, the QR generator in the donate page is one of the coolest features I have seen. Good work! It would be cool to have QR codes printed on the invoices that link directly to students' accounts to make payment like the link generated under the "someone else paying" link. I could see how this would be helpful for schools that mail out paper invoices (we do mail outs for delinquent accounts).