Ensure proper translation of the about dialog title

Note that GTK+ sets a default title of _("About %s") on the dialog
window (where %s is replaced by the name of the application, but
in order to ensure proper translation of the title, applications
should set the title property explicitly when constructing a
GtkAboutDialog

https://developer.gnome.org/gtk3/stable/GtkAboutDialog.html

src/callbacks.cpp

@@ -201,6 +201,7 @@ cb_about (GtkAction *action, gpointer data)
    gtk_show_about_dialog (
        GTK_WINDOW (procdata->app),
        "name",               _("System Monitor"),
        "title",              _("About System Monitor"),
        "comments",           _("View current processes and monitor system state"),
        "version",            VERSION,
        "copyright",          _("Copyright \xc2\xa9 2001-2004 Kevin Vandersloot\n"