Add 'Load Folder' menu option

src/yuzu/main.h

@@ -123,6 +123,7 @@ private slots:
     void OnGameListLoadFile(QString game_path);
     void OnGameListOpenSaveFolder(u64 program_id);
     void OnMenuLoadFile();
+    void OnMenuLoadFolder();
     /// Called whenever a user selects the "File->Select Game List Root" menu item
     void OnMenuSelectGameListRoot();
     void OnMenuRecentFile();