[SPARK-8704] [ML] [PySpark] Add missing methods in StandardScaler

Add std, mean to StandardScalerModel
getVectors, findSynonyms to Word2Vec Model
setFeatures and getFeatures to hashingTF

Author: MechCoder <manojkumarsivaraj334@gmail.com>

Closes #7086 from MechCoder/missing_model_methods and squashes the following commits:

9fbae90 [MechCoder] Add type
6e3d6b2 [MechCoder] [SPARK-8704] Add missing methods in StandardScaler (ML and PySpark)