Implement Delete operation in AccountPanel contextual menu

Fix a bug in a SQL request
Use nbCategories in AccountPanel to prevent buffer overflow

src/model/Database.hpp

@@ -46,7 +46,7 @@
 	if (!query.exec(req))						\
 	{								\
 	    QMessageBox::critical(0, _("Error"), _("Update failed !\n") + req); \
-	    std::cerr << __FUNCTION__ << "\n" ;				\
+	    std::cerr << __FUNCTION__ << " " << __FILE__ << " " << __LINE__ << "\n" ; \
 	    std::cerr << req.toStdString() << "\n" ;			\
 	    std::cerr << query.lastError().text().toStdString() << "\n" ; \
 	    code_if_fail;						\