show date of news

We used to use the date of each news-item as the heading, but after converting them, I standardized the headings to be something more meaningful.

But it's still useful to see the date, so let's still display that.

This takes a slight shortcut; it specializes the news-version of single, but leaves dates in the _default version of list.html. This is because dates only makes sense for news, and we don't have any lists of non-news.

Closes: #9 (closed)