Draft: "Blog posts" instead of "News". Adapted Buttons at bottom of front page.

rename to blog posts, buttons according to https://gitlab.hzdr.de/hifis/overall/hifis.net/-/issues/310#note_1408462

• Filter for nothing anymore (yet "news")
• Decide on whether to remove "news" tag altogether; or instead remove only from some
• need to redirect all news links to corresponding posts links
• rss feed is still called news.xml, but I think that's fine.