Obstacle detection added.
- NEW: UltrasonicSensor: added setIsObstacleDetectionActive() & isObstacleDetected()
- NEW: added UltrasonicSensorAdapter interface, notifyObstacleDetectionChange()

Signed-off-by: Dieter Niklaus <dieter.niklaus@gmx.net>
Merge remote-tracking branch 'remotes/origin/branch-obstacle-detection'