qt: Send dialog status to VM-manager & fix pause

- Manager is notified of modal dialogs blocking the main window.
- Pause command from manager uses action to prevent desyncing pause status
in the menus and toolbar.

src/qt/qt_mainwindow.hpp

@@ -50,6 +50,7 @@ signals:
 public slots:
     void showSettings();
     void hardReset();
+    void togglePause();
 private slots:
     void on_actionFullscreen_triggered();
     void on_actionSettings_triggered();