Adds

rank, recommendUsers and RecommendProducts to MatrixFactorizationModel in PySpark.

Author: MechCoder <manojkumarsivaraj334@gmail.com>

Closes #5807 from MechCoder/spark-6257 and squashes the following commits:

09629c6 [MechCoder] doc
953b326 [MechCoder] [SPARK-6257] MLlib API missing items in Recommendation