Send empty clicked object result

Send empty clicked object result

- Issue:
Voice touch app did not clear the tooltip when user says 'back' or
'referesh'.

- Solution:
Current mmi-manager did not send result to client app, but just sends
output event to output modality when the utterance is pre defined
command. Thus, client app can not handle pre-defined command action
situation. This patch sends result of pre-defined command to client app.
Through this patch, client app can handle this special situation.

Change-Id: I560276bfa230e2171b3d79ed6a69f260a6a239be
Signed-off-by: Suyeon Hwang <stom.hwang@samsung.com>