NEW Add statistics for interventions module

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

htdocs/comm/propal/stats/index.php

htdocs/commande/stats/index.php

htdocs/core/class/html.formpropal.class.php

htdocs/core/modules/modSupplierProposal.class.php

htdocs/fichinter/card.php

htdocs/fichinter/class/fichinterstats.class.php

htdocs/fichinter/stats/index.php

htdocs/install/mysql/tables/llx_propal.sql

htdocs/install/mysql/tables/llx_supplier_proposal.sql

htdocs/langs/en_US/interventions.lang

htdocs/langs/en_US/propal.lang