Add EC sales list
Following the discussion https://groups.google.com/d/topic/tryton/Gc_1ivnZl0U/discussion and according to http://www.vatlive.com/eu-vat-rules/eu-vat-returns/ec-sales-list-esl/, the EC sales list is a common requirement in Europe even if it takes different shape.
I propose to create a common account_eu module which provides the basic to implement this report (and in the future others common).