Avoid detection of private IP addresses

ValidationIpHelper::getRequestIP() scans the following $_SERVER vars:
HTTP_CLIENT_IP, HTTP_X_FORWARDED_FOR, HTTP_X_FORWARDED,
HTTP_X_CLUSTER_CLIENT_IP, HTTP_FORWARDED_FOR, HTTP_FORWARDED,
REMOTE_ADDR (in this order).
If the client is visiting the website via a proxy server located in his
own private network the function may return his local private IP
address.

Let's change this behavior, trying to detect only public IP addresses
(but still returning the private IP address if no public address is
found).
Merge pull request #1078 from mlocati/fix-ip-detection

Avoid detection of private IP addresses