For the purchase order sending mail, update the partner language to en_US, and change it back once the PDF generated
1.Add purchase.order.comments field
2.When changing purchase.order.minimum_planned_date, also set the sotck.pick.min_date
3.metro_purchase:show the purchase orders as red and bold in the list page, when the minimum_planned_date less than now
4.metro_stock:show the stock in orders as red and bold in the list page, when the min_date less than now
5.metro_stock:override the stock.picking._set_minimum_date,_set_maximum_date, to update the stock_move.date_expected when update min_date