CDAP-538: Ported procedures of WordCount app to services.

@ParthGandhi The WordCount app has been updated with services instead of procedures, please take a look.
So if limit=0 is passed or no limit is passed, we'll have a limit of 10? I think we should differentiate between the two. Probably can use `Integer limit` instead of `int limit` and if `null` use default limit? Not sure how netty-http is handling this.