QR Code overlays

We have added a new functionality. Ability to add an overlay image over QR code. With this functionality we can do something like image bellow.

![QR Code BBC](http://www.flyteblog.com/wp-content/uploads/2011/01/bbc-logo-in-qr-code.gif)

We forked from [meinfernbus/MopaBarcodeBundle](https://github.com/meinfernbus/MopaBarcodeBundle), because he already implemented the options for sizes.