removed some icons and menus items : new, cut, copy, paste
removed AboutQt item from the menu
removed the CROSSCOMPILE_TO_WIN_USING_MXE compilation option
MainWindow::about() displays the internal messages if the (new) compilation option DISPLAY_INTERNAL_MESSAGES_IN_HELP_MENUITEM has been defined.
Merge branch 'feature45' into dev
o  cleaned up the ui (removed useless menu+icon items)
o  MainWindow::about() may now display the internal messages
o  new compilation option : DISPLAY_INTERNAL_MESSAGES_IN_HELP_MENUITEM