added software renderer. split common functions prev.

in gleswidget to renderstack (a QStackWidget), which in
turn calls an actual renderer. added ability to target GLES
directly, but this is maybe uneeded.

src/qt/qt_mainwindow.hpp

@@ -52,6 +52,9 @@ private slots:
     void on_actionHard_Reset_triggered();
     void on_actionRight_CTRL_is_left_ALT_triggered();
     void on_actionKeyboard_requires_capture_triggered();
+    void on_actionHardware_Renderer_OpenGL_ES_triggered();
+    void on_actionHardware_Renderer_OpenGL_triggered();
+    void on_actionSoftware_Renderer_triggered();
 
     void refreshMediaMenu();
     void showMessage_(const QString& header, const QString& message);
@@ -60,6 +63,7 @@ private slots:
 protected:
     void keyPressEvent(QKeyEvent* event) override;
     void keyReleaseEvent(QKeyEvent* event) override;
+
 private:
     Ui::MainWindow *ui;
     std::unique_ptr<MachineStatus> status;