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/subsonic/subsonicurlhandler.h

@@ -54,6 +54,8 @@ class SubsonicUrlHandler : public UrlHandler {
   typedef QPair<QByteArray, QByteArray> EncodedParam;
   typedef QList<EncodedParam> EncodedParamList;
 
+  void Error(const QString &error, const QVariant &debug) {}
+
   SubsonicService *service_;
 
 };