Fixed bug from last commit (sorting paramMap by parameter names in toString).  Fixed bug in persisting logreg data.  Added threshold_internal to logreg for faster test-time prediction (avoiding map lookup).
Fixed issue with logreg threshold being set correctly
Updated docs.  Added LabeledPointSuite to spark.ml
* Changed semantics of Predictor.train() to merge the given paramMap with the embedded paramMap.
* remove threshold_internal from logreg
* Added Predictor.copy()
* Extended LogisticRegressionSuite
added train() to Predictor subclasses which does not take a ParamMap.