Add QR code in prototype player's starting points menu panel

When playing a prototype link, it would be nice to be able to quickly load it into a client’s phone without having to get the app. Furthermore, many mobile web prototypes really need to be played inside the browser to convey the full experience.

Adding a QR code of the prootype URL would be great. Looks like there is plenty of room in the navigation panel for interaction starting points on the left.