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/collection/collectionmodel.h

@@ -99,6 +99,8 @@ class CollectionModel : public SimpleTreeModel<CollectionItem> {
     GroupBy_Disc = 12,
     GroupBy_OriginalYearAlbum = 13,
     GroupBy_OriginalYear = 14,
+    GroupBy_Samplerate = 15,
+    GroupBy_Bitdepth = 16
   };
 
   struct Grouping {