Improve album cover searching and cover manager, use HttpStatusCodeAttribute and QSslError for services

- Improve album cover manager
- Change art_automatic and art_manual to QUrl
- Refresh collection album covers when new album covers are fetched
- Fix automatic album cover searching for local files outside of the collection
- Make all Json services check HttpStatusCodeAttribute
- Show detailed SSL errors for Subsonic, Tidal and Qobuz

src/core/systemtrayicon.h

@@ -47,7 +47,7 @@ class SystemTrayIcon : public QObject {
   // Called by the OSD
   virtual void ShowPopup(const QString &summary, const QString &message, int timeout) {}
   // If this get's invoked with image_path equal to nullptr, the tooltip should still be shown - just without the cover art.
-  virtual void SetNowPlaying(const Song &song, const QString &image_path) {}
+  virtual void SetNowPlaying(const Song &song, const QUrl &cover_url) {}
   virtual void ClearNowPlaying() {}
 
   virtual bool MuteEnabled() { return false; }