Propose a base implementation for sales orders canceled on a backend.
* sale_order.cancelled_in_backend means a sale order has been cancelled on the backend * when sale_order.cancelled_in_backend is set to True, it tries to automatically cancel the SO * when such a SO is cancelled, sale_order.cancellation_resolved is set to True * the user has a button to set sale_order.cancellation_resolved to True without cancelling it * search filter to display the SO to cancel * Sales exceptions when a SO has been canceled on the backend * SO can have a parent (logic of the parents is to implement in the connectors) * Sales exception when a parent SO has been canceled on a backend * adds notifications to inform the user what is happening