Config::FailedToLoad.connect (boost::bind (&App::config_failed_to_load, this));
Config::Warning.connect (boost::bind (&App::config_warning, this, _1));
Config::FailedToLoad.connect (boost::bind (&App::config_failed_to_load, this));
Config::Warning.connect (boost::bind (&App::config_warning, this, _1));