Allow user to edit planned date on waiting shipments
Since #9264 (closed) the systems reschedules the past waiting shipments, but sometimes the user may want to update the planning manually (because he know that may be a delay or accord with the customer a different date).
Although this is currently possible, the user needs to move the shipments back to draft, update the planned date and then date move back the shipment to waiting. This is not intuhitive and the user sometimes misses this feature because the field is readonly. So it will be better to make it writeable on waiting state.