Introduce config params to use latest EH client, control request prefetch size, batch size

[raviperi]

of events received per call.

-Refactor the code to group classes more appropriately
-Remove redundant types
-Javadoc comments where applicable
-Preftch config parameter to dictate EH prefetch count
-config parameter to introduce sleep between spout's nexttuple calls
-config parameter to retrieve a batched number of events per call to EH
(opposed to single event)
-New data scheme to group event payload and audit params into a single
type, and expose the single type as the only tuple field to downstream
bolts.