Add a DEP-14 diagram

The diagram comes in two formats:
 - SVG with editable text (apertis-dep-14-gitlab.svg)
   This is the primary source.
 - SVG with texts as paths (apertis-dep-14-gitlab-curves.svg)
   This is generated from the primary source; it is a preferred
   format for embedding as a figure in a document, since it
   doesn’t depend on the availability of fonts or the renderer’s
   ability to render them correctly.

Signed-off-by: Andrej Shadura <andrew.shadura@collabora.co.uk>