refactor(news): save articles through a use case and the repository
SaveArticleUseCase validates the form and writes the article with its text for the search; the form keeps its addresses and its template. Two answers change on the way: a code taken at the root is refused as in a section rather than ending in an error of the database, and a date that is not one is refused rather than ending in an error of the server. The dates are no longer escaped on their way in.