Give QRdetect single QR code option.

[ryanpeach]

I built QRdetect as generally as possible, able to detect ALL QR codes in an image. However, this is very complex and for a high number of QR codes it would greatly slow down video processing. GIve it a variable with a default value of one and an "all" value of -1 which allows the user to decide how many QR codes they want to detect max.

Also, implement QR decoding in a different file, will probably need to be different for java vs c++.