[SPARK-4435] [MLlib] [PySpark] improve classification

This PR add setThrehold() and clearThreshold() for LogisticRegressionModel and SVMModel, also support RDD of vector in LogisticRegressionModel.predict(), SVNModel.predict() and NaiveBayes.predict()
Please update the doc for linear binary classification model. Do we need `Experimental` tag here? It is a private class.