PAM authentication feature + several bugfix

  * Fixed cannot input domain in 'DNS search domain' field
  * Fixed cannot input multiple entries separated with commas
  * Fixed log entries missing for date from 1 to 9
  * Restricted 'Common Name' field in certificate tab to alphanum
  * Fixed iptables rule not added upon boot/reboot
  * Refined iptables to remove previous rule before adding new rule
  * Added 'PAM authentication' checkbox