CDAP-610: Port TwitterSentiment app to use Services instead of Procedures

@ParthGandhi @sreevatsanraman please review
I know I suggested having multiple endpoints with default values, but Terence has implemented "@QueryParam" in https://github.com/caskdata/netty-http/pull/9. So maybe we should hold off on this till that gets merged, so we can use it. That would make the implementation closer to the Procedure.