Optimize FLOC banner integration

This patch reworks various aspects for the FLOC banner to be simpler to
copy and easier on SEO.

Search engines don't like hidden content. Therefore moving the HTML from
the template to the JS that was used to make it show up, makes a lot of
sense. The usage of `insertAdjacentHTML()` can be considere safe, since
no dynamic content is injected.

It improves the commit 7896142b why
holds all basic reasoning behind implementing this banner in first
place.