Export cancellation of sales orders to Magento

When a sales order is cancelled on Odoo, a job to export the sales
order on Magento is generated.

When the button to create a new sales order from the canceled one
is used on Odoo, the sales order on Magento is reopened.

The job does not use the 'sales_order.cancel' Magento API method
because this method prevents to reopen the order later (it changes
the 'state' field). Instead, it uses the 'sales_order.addComment' that
change the 'status' of the order and allow to reopen the status later.

 - [ ] Needs #9 to be merged before