Add slugified title to urls in sitemap.xml

Also change routing a bit to allow title in contents urls

The title slug is generated in postgres, but it doesn't really work with unicode characters.

I tried using `cnxarchive.utils.slugify` and the time to do 50000 `cursor.execute("SELECT uuid||'@'||concat_ws ...` to `xml.add_url('http://%s/contents/...` is about 127s while doing it in postgres is 79s.  I don't know if correctness is more important or performance.