Track recording service handles the status of recording: track's id, pause and GPS status.

Created an interface for all components that want to know about recording status through the service.
All interface's methods are optional so every component can implement what they need.
Fixes #388.

src/main/java/de/dennisguse/opentracks/TrackController.java

@@ -129,7 +129,7 @@ public class TrackController implements View.OnTouchListener {
             buttonDelay = () -> {
                 view.sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);
                 view.performClick();
-                callback.recordStart(); //TODO Should be recordPause();
+                callback.recordPause();
 
                 transition.resetTransition();
 
@@ -239,7 +239,7 @@ public class TrackController implements View.OnTouchListener {
 
     public interface Callback {
         void recordStart();
-
+        void recordPause();
         void recordStop();
     }
 }