Forbid access above static folder

[fcollonval]

Are you sure it is a good idea to remove the security check under_frontend_dir(frontend_dir, path)?
The reason for this check is not to allow requesting files that are not under the frontend_dir directory.

Originally posted by @hbcarlos in #96 (comment)

[fcollonval]

Closing as this is ok. The URL built by the browser cannot include dotted segments.