ftp: add support for directory listing without MLST

The current version of the ftp browser requires the MLST extension introduced to the ftp protocol in RFC 3659 (in 2007) to differentiate between files and folders in a file listing.

The default FTP daemon included in ubuntu vsftpd (version 3.0.3-12) does not support this extension leaving all media listed at the "unknown" state. However, competing implementations of the FTP protocol like in Cyberduck can well differentiate. VLC should be able to do the same.