New: Add graphical box for turnover and proposal

htdocs/commande/stats/index.php

htdocs/compta/facture/list.php

htdocs/core/boxes/box_graph_orders_permonth.php

htdocs/core/boxes/box_graph_orders_supplier_permonth.php

htdocs/core/boxes/box_graph_propales_permonth.php

htdocs/core/modules/modFournisseur.class.php

htdocs/core/modules/modPropale.class.php

htdocs/langs/en_US/suppliers.lang

htdocs/langs/fr_FR/suppliers.lang