Allow admin to trigger process on processing state
This [1] shows that some miss-configuration can lead to a situation that are difficult for the end-user to correct. Because the processing is done in the queue (and the queue does not restart jobs on purpose) and error in the processing stop the workflow. So I think we should give a mean to the administrators to re-trigger the process method to fix the workflow (or to see the error message).
[1] https://discuss.tryton.org/t/article-created-as-asset-and-not-goods-does-not-generate-invoice-when-shipment-received-if-accounting-category-unset/1131