refactor WM_COMMAND messages handling in MDI frames to avoid duplicating code unnecessarily and generally streamline it; added possibility to use custom menu commands in the "Window" menu and specifying accelerators for them now works too (show this in the sample); finally added standard ids for the MDI window menu commands

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@58462 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

samples/mdi/mdi.h

@@ -53,6 +53,8 @@ private:
     void OnNewWindow(wxCommandEvent& event);
     void OnFullScreen(wxCommandEvent& event);
     void OnQuit(wxCommandEvent& event);
+    void OnCloseAll(wxCommandEvent& event);
+
     void OnClose(wxCloseEvent& event);
 
     wxTextCtrl *m_textWindow;