[New] Implemented ServiceHandler with Privilege validation

Performing a Service is as simple as this:
  GreetingService greetingService = new GreetingService();
  GreetingArgument greetingArgument = new GreetingArgument();
  greetingArgument.name = "Robert";
  GreetingResult greetingResult = serviceHandler.
        doService(null, greetingService, greetingArgument);
  assertThat(greetingResult.getGreeting(), 
        containsString("Hello Robert. Nice to meet you!"));