TrackRecordingService uses LiveData to transfer data.

Replaces pull from UI layer.

Fixes #173.

src/main/java/de/dennisguse/opentracks/content/TrackDataHub.java

@@ -78,6 +78,7 @@ public class TrackDataHub {
     private EGM2008Utils.EGM2008Correction egm2008Correction;
 
     private boolean started;
+    //TODO Check if this is needed.
     private HandlerThread handlerThread;
     private Handler handler;