ENH: Expose K parameter to control number of neighbors used in KNN machine learning. Also expose IsRegression parameter.

ENH: Add a parameter IsRegression in BoostMachineLearningModel to indicate if it is a regression model or a classification model.

ENH: add ValidateImagesClassifier application to validate a classification model obtained with TrainMachineLearningImagesClassifier.

ENH: Add an ImageClassifier application that classifies an image using a model obtained with TrainMachineLearningImagesClassifier application.