Set secret files permissions for root only. Refs #1957

/etc/ipsec.secrets RPM default permissions are 0600, to keep secret
passwords secure. Also NSS DB private RSA key password must be kept
secure in /etc/ipsec.d/nsspassword.
VPN IPsec UI module. Refs #1957

This first version of the web UI module controls ipsec and xl2tpd
daemons execution, changes RoadWarriors subnet assignment and IPsec
authentication method (PSK or RSA). The nethserver-ipsec-save event
has been defined for these purposes.