Ftp statistics features

Hi,

I add the ftp traffic support for pure-ftpd.

• Ftp statistics display per hostname in site section (traffic in and out)
• Ftp_traffic table (creation and update patch upd_0081.sql)
• Cronjob
• Actually pure-ftpd log rotation are configured with /etc/logrotate.d/pure-ftpd-common
• Maybe replace that per Ispconfig log rotation ?
• Api function for ftp traffic

THanks