[16.0][IMP] sale_stock_available_to_promise_release mto availability_status

[santostelmo]

When stock becomes available for is_mto product,, sale order line availability status should reflect that status. Currently nothing happens in that circumstances as the status always stays in on_order even if there's stock available.

Also standard is already providing a computed field is_mto => _on_order_route can be dropped.