Add referrer to QR code generated on label.

Adding a referrer to the link generated for the QR code will allow us to change the interface if a user comes in from a QR code scan. It will also allow us to track if QR codes placed on tools are being used.

One potential changed UI when visiting via the QR code, would be to make it easier to borrow or a return the tool. Maybe by placing a button closer to the top of the page.