Add new APIs about service state information

Add new APIs about service state information

- Requirement:
An application needs state of TTS service in order to check whether the
TTS service is able to handle the request of the application.

- Solution:
This patch adds new APIs for checking state of TTS service. Through
these new APIs, applications which use TTS can check the state of TTS
service and handle the TTS request according to the state of TTS
service.

Change-Id: I7fbbf3f9e316b91468423c26c38452383498cf34
Signed-off-by: Suyeon Hwang <stom.hwang@samsung.com>