code: public RequestToken logout(String registration, int flags, BaasHandler<Void> handler) {
          BaasBox box = BaasBox.getDefaultChecked();
          LogoutRequest request = new LogoutRequest(box, this, registration, flags, handler);
          return box.submitAsync(request);
      }
docs: Logouts the user from the specific device. After this call completes no current user
  is available. {@link BaasUser#current()} will return <code>null</code>.
  And on this device the user will not receive any new message from google cloud messaging.
  
  @param registration a registration id to remove
  @param flags {@link RequestOptions}
  @param handler      an handler to be invoked upon completion of the request
  @return a {@link com.baasbox.android.RequestToken} to handle the async request