Bluetooth: use TrackRecording handler for callback.

Otherwise the thread is not defined and a SecurityException may be triggered when inserting data into the ContentProvider.
Sadly, below API26 this needs to be done manually.

Fixes #1165.

src/androidTest/java/de/dennisguse/opentracks/services/handlers/TrackPointCreatorTest.java

@@ -32,7 +32,7 @@ public class TrackPointCreatorTest {
     @Before
     public void setUp() {
         subject = new TrackPointCreator(locationHandler, server);
-        subject.start(context);
+        subject.start(context, null);
     }
 
     @After