added a prediction overload call where is possible to retrieve all the l...

Added an overload to the prediction call to FaceRecognizer. 
Retrieve all scores and labels, not just the best.
Scores and labels are sorted by lower (best) to highest.
@bnascimento , is there any reason why you try to remove this functionality from the `cv::FaceRecognizer`???
(I mean `cv::FaceRecognizer2` and the methods working with labels info!)