added iptables rule for ntp
removes validation for authenticated tor hidden service users
added localhost to localhost udp iptables rules for monitor server
Merge pull request #266 from dolanjs/dolanjs-ATHS-user-validation-fix

* closes #266
* hotfix
Merge branch 'ntp-iptables-rule' of https://github.com/dolanjs/securedrop into dolanjs-ntp-iptables-rule
Merge pull request #264 from dolanjs/ntp-iptables-rule

* closes #264
* hotfix
Fix typo in x-xss-protection header