Added service that listens for gestures.

Added the GestureLauncherService that listens for camera launch gesture
and starts the camera app.
OEMs need to specify the sensor type of the camera launch gesture in
their overlays.
In the future, we can add more gesture support in this service.

Change-Id: I0769e7ca71e08bd9159aacf29bdcefd316efd2f0