Ftp statistics feature

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

See merge request !266

fixed db.quota stats



See merge request !262

Master



See merge request !261

This reverts commit 9d3f2bbc.

This reverts commit aab7e05b.

some more filter_var for ipv4 / ipv6



See merge request !260

use filter_var instead of regex for ip-addresses



See merge request !259