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.
This has nothing to do with our APIs. This is part of the HTTP specification. 

http://www.w3.org/Protocols/rfc2616/rfc2616-sec6.html#sec6.1.1
"2xx: Success - The action was successfully received, understood, and accepted"