[AudioSystem][IVI]: Implementation of Tizen Audio System/Control API.

This commit implements proposed Tizen System Volume API on xwalk:
  https://wiki.tizen.org/wiki/User:Tanuk/AudioSystemAPI
This commit also includes a demo application that demonstrates the
usage of the api.

This enables to write volume control/settings/mixer type of web applications
using xwalk.

BUG=XWALK-1330
So I guess better declare `volume_control_` as `double`?