Concept documents express an idea or plan on which Apertis is working,
and will shape its future. However, over time plans change and some
concept documents are not longer in the roadmap.

Since the ideas in those documents are still valid and there is value
in keep, them move them to a new "archive" section, so they can still be
accessed without confusing the audience.

Signed-off-by: Walter Lozano <walter.lozano@collabora.com>