Wrong alternate links (at least on posts)

Like in #643 (closed), the hreflang links only point to f-droid.org/<lang> and not to the relevant page, at least when reading news items. It got fixed for packages and pages with permalinks (should be tutorials and docs from the default value in _config.yml and some single pages)

For every other page, this is caused by using page.permalink instead of page.url (see !1167 (merged), where I fixed it for the canonical URLs and og:url).