Fix OPENDJ-43 (Synchronous Connection decorator implementations should not use AsynchronousConnections) and OPENDJ-328 (Make it easier to implement connection decorators).
Merged AsynchronousConnection interface into Connection and added "Async" suffix to asynchronous operation methods so that they can be easily distinguished from their synchronous counterparts. Added AbstractAsynchronousConnection class which facilitates development of new Connection implementations whose underlying implementation is asynchronous.