Instead of Java Vertx Futures, hand over Promises

[Narigo]

This would enable us to write:

def start(p: Promise[Unit]) = {
  doSomethingAsyncReturningAFuture() map { result =>
    p.success()
  } recover { ex =>
    logger.error("problem at start up!", ex)
    p.failure()
  }
}

a) We wouldn't need the Future class at all.
b) It would be more towards the Scala-way
c) Users cannot overwrite the Futures failure handler during startup. This is safer than the Java API approach (hoping the dev doesn't do stupid things ;)).

[galderz]

Hmmm, we already have an issue to provide a Future/Promises based API, see #16. We should focus related to providing such API there? :)