Make sure service also runs in background after first app start.

Previously, it would be stopped when exiting the activity due to no
call to `startService()`.

src/main/java/com/nutomic/syncthingandroid/activities/SyncthingActivity.java

@@ -33,6 +33,7 @@ public class SyncthingActivity extends ActionBarActivity implements ServiceConne
     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
+        startService(new Intent(this, SyncthingService.class));
         bindService(new Intent(this, SyncthingService.class),
                 this, Context.BIND_AUTO_CREATE);
     }