Adapt news urls (pt)

See issue #25 for discussion.

This implements the url changes that require some special treatment, namely the news archive and the news feed (due to connected changes in the news plugin etc.).

Local build works fine. No broken internal links are introduced.

Keeping the old links available could be done with rewrite rules, such as possibly

    rewrite ^/pt/noticias-recentes/(.*)$ /pt/news/$1 permanent;
    rewrite ^/pt/feeds/noticias.rss$ /pt/feeds/news.rss permanent;