Fancy url

This PR provides an option to generate a media file URL adapted for SEO instead of the classic cryptic pattern.
The new pattern is: /media/{format}/{id}/{name}

For example: http://domain.tld/uploads/media/mycontext/0001/01/4e28dc8cde1cf296b813e16c493844793135df77.png will become http://domain.tld/media/reference/1/home.png

If the `fancy_url` option is enabled, Twig's functions will use automatically this new URL pattern.