Merge all the content from announcements to news-items.
Most of the announcements had an associated news item that said
little more than "there is an announcement, read it in the announcements".
Since news items have proved to be the thing-we-do-more-and-longer,
merge contents of announcements back to the news items that originally
pointed to them, and now point the announcements to the news items instead.
The news items have a nice paginated history.
TODO: figure out 302 redirects for these announcement pages.