Starting towards a generic API so that `JsonNode` isn't exposed through the client

DELETE endpoint will return void b/c the structure of the JSON returned is really unrelated to the delete.  Generics don't make sense.
 - one can make the case that a class `DeleteResponse` or something could be created to return the results, if it's useful
Bettering the generic interface so that there aren't generics hacks in the implementation
Changing package structure to be more modular.
Merge pull request #6 from CruGlobal/feat/3

Generic EntityEndpoints