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/savedgroupingmanager.cpp

@@ -110,6 +110,12 @@ QString SavedGroupingManager::GroupByToString(const CollectionModel::GroupBy &g)
     case CollectionModel::GroupBy_Bitrate: {
       return tr("Bitrate");
     }
+    case CollectionModel::GroupBy_Samplerate: {
+      return tr("Sample rate");
+    }
+    case CollectionModel::GroupBy_Bitdepth: {
+      return tr("Bit depth");
+    }
     case CollectionModel::GroupBy_Disc: {
       return tr("Disc");
     }