Fix setting output/device for Xine and VLC backend

- Fixed setting output and device on Xine and VLC backend
- Fixed track slider for Xine, VLC and Phonon
- Improved backend settings to better support multiple backends
- Added group by samplerate and bitdepth in collection
- Fixed crash on exit when existing instance of the application is already runnung caused by NVIDIA driver
- Changed Q_OS_MAC to Q_OS_MACOS

src/device/ilister.cpp

@@ -58,6 +58,8 @@ void iLister::EventCallback(const idevice_event_t *event, void *context) {
     case IDEVICE_DEVICE_REMOVE:
       me->DeviceRemovedCallback(uuid);
       break;
+    default:
+      break;
   }
 }