Add new class for managing activated mode

Add new class for managing activated mode

- Requirement:
TTS server should manage current activated mode information. This
information for the service engine application to help decide behavior
of the application.

- Solution:
In order to store and manage currently activated mode information, this
patch adds new class. This new class only manages the currently
activated mode information, and other modules can get this information
through the methods of this class.

Change-Id: I13d47ebcf3b28c18583ac3dbe14302af0438bf94
Signed-off-by: Suyeon Hwang <stom.hwang@samsung.com>