* add redirects from old urls
* old manuals are now served as stable
* and unstable manuals were added
* <link rel="cannonical" url=".." /> was added not to confuse search
  engines

change manual location and add unstable version

As discussed

This *strongly assumes* that the SVG will be available, and also assumes
that the DOM and styles are ready to embed the SVG at this location.

Additionally, yet unwritten, another component will be needed at the
location where the "pane" with the actual demo will be shown.

Finally, JavaScript will be used to make the pane show up properly when
activated.

Note that this is a manual edit of the template, for testing purposes.

This should be made a part of the demo processing tooling.

This reverts commit 27ea2e2.

It has been verified that recent iOS versions don't need that anymore.

Though only show with `-debug` body class

This can be used to better document responsive bugs by showing at which
level the user saw the issue.

This way we can ensure all usage of the component are coherent with each
other.

See, there's absolutely nothing specific to the demo panes! It's a
generic behaviour for panes.

Using a BLOCK like this is the only way we will be able to manage having
misc. contributors edit the site. No soup of DOM as an internal detail.

This is a proposed feature, not implemented yet.