Refactored generateDocument functions

htdocs/comm/propal/class/propal.class.php

htdocs/commande/class/commande.class.php

htdocs/compta/facture/class/facture.class.php

htdocs/contrat/class/contrat.class.php

htdocs/core/class/commonobject.class.php

htdocs/expedition/class/expedition.class.php

htdocs/livraison/class/livraison.class.php

htdocs/projet/class/project.class.php

htdocs/projet/class/task.class.php