Spark Integration: SparkPageRank now uses Service

Added a simple service to SparkPageRank example application to showcase how to use services in Spark.

@anew : Please review. Thanks.
Agree but my idea was that if we change encoding to something else (the possibility is rare) we will just need to modify one thing and not everywhere. 
If its not a really bad thing then I will like to keep this as it is now else please let me know.