[FIX] website_quote: forbid to define a quote template on a sale order

Defining a quote template may change the product list. The field template_id is now editable
only when the sale.order is in draft or sent state.
[FIX] account: res_config: gain/loss exch. account onchange

Commit f4e350ca3 defined an `onchange_company_id` method, never executed
because another `onchange_company_id` was defined below. Merged the first
in the second.