[FIX] product: allow user to set price at template creation

The lst_price field on product.template is a related to list_price. As we do not allow to set a value for related fields at creation (see orm.py , L4180), we display the list_price instead (float field).
On the product.product form, we display the lst_price (function field, readonly) as we don't want to allow changing the template price from the product. opw 609497