Rewire more of Sailfish frontend into new backend

This should encompass most simple things, besides some larger, trickier
things, like the video streams and the now-broken userdata

core/include/JellyfinQt/credentialmanager.h

@@ -123,7 +123,6 @@ public:
 
 private:
     QString urlToGroupName(const QString &url) const;
-    QString groupNameToUrl(const QString &group) const;
     QSettings m_settings;
 };