Several new things !

- General : syntax checking of the configuration file *(thanks to Micht69)*
- General : check PHP version (5.3+) *(thanks to Gilles)*
- General : add *check_updates* setting to the config file to enable or not the checking for updates
- General : add *auto_refresh* setting to the config file to automatically reload page each x seconds *(thanks to sebastienserre and Aranud)*