The name "action menu" was made because it used to be where people hit
like button, comment and send webmentions. Now it's only for
webmentions.

- remove inject-footnotes.js, use a partial that receives `.Content` and
does the injection statically
- use a `utils/render` partial, as custom "render hook"
- reuse `content` partial for all pages

component, hence `.Site.LanguagePrefix` gives nothing.