Consider if invariant in Crm::Order is really needed

[pjurewicz]

After dealing with #225, it is possible for Ordering::Order to return to a draft state after being rejected.
Since, these two commands are called together:

command_bus.(Ordering::SubmitOrder.new(order_id: params[:order_id]))
command_bus.(Crm::AssignCustomerToOrder.new(customer_id: cookies[:client_id], order_id: params[:order_id]))

It causes a problem when resubmitting rejected Order because of this invariant:

raise CustomerAlreadyAssigned if @customer_id