[VIndex] Optionally serve static files at the http root

Just for convenience, making it possible to just reverse proxy an entire (sub)domain directly to vindex, without having to configure separate paths for an index.html, favicon, robots.txt, etc, or having to configure forwards for /vindex/, /outputlog/ and possibly /inputlog/. An http handler could be registered when a cli flag is present that references a directory with the files to serve.