feat: option to disable gallery looping

This change is sponsored by @superuser7777

Related: https://github.com/BLumia/pineapple-pictures/issues/153

app/mainwindow.h

@@ -110,6 +110,7 @@ private slots:
 
 private:
     bool updateFileWatcher(const QString & basePath = QString());
+    void updateGalleryButtonsVisibility();
 
 private:
     ActionManager *m_am;