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

ext/libstrawberry-common/core/workerpool.h

@@ -228,7 +228,7 @@ void WorkerPool<HandlerType>::DoStart() {
 
   QStringList search_path;
   search_path << qApp->applicationDirPath();
-#ifdef Q_OS_MAC
+#ifdef Q_OS_MACOS
   search_path << qApp->applicationDirPath() + "/../PlugIns";
 #endif