public class OpenCVFilterFaceTraining.OpenCVClassifier
root is the location on the file system where this classifier is supposed
to work and classify into sub directories.
A subclass is the same as a directory who's name is a "label"
it keeps track of the set of subdirectories and the number of image files
to train from. If the number of files change, or the number of directories
without underscore - it will likely cause a 're-train'