Make predict() return "Undetected" in the classification estimator if confidence is below threshold

**Use case: flower recognition**
_Input:_ flower photo
_Output:_ flower name

Right now if you input a flower that is not among the classes, predict() will return the one closest to it which is wrong. The right would be telling the user that it was not recognized. One way to do it is making the estimator produce a confidence float [0-1]. Then make predict() accept a confidence threshold along with the data, which if not surpassed returns "Unrecognized".