Move GPSManager into SensorManager.

Includes Bugfix: SensorManager might not have been stopped.

Part of #1424.

src/main/java/de/dennisguse/opentracks/services/handlers/GPSManager.java

@@ -30,7 +30,7 @@ public class GPSManager implements SensorConnector, LocationListenerCompat, GpsS
 
     private final String TAG = GPSManager.class.getSimpleName();
 
-    public static final String LOCATION_PROVIDER = LocationManager.GPS_PROVIDER;
+    private static final String LOCATION_PROVIDER = LocationManager.GPS_PROVIDER;
 
     private final TrackPointCreator trackPointCreator;
     private Context context;