IPv4 vs IPv6 issues in the StatsAccess event listener

If an admin configures `Imbo\EventListener\StatsAccess` in the following way:

```php
return array(
    'eventListeners' => array(
        'statsAccess' => array(
            'listener' => 'Imbo\EventListener\StatsAccess',
            'params' => array(
                'whitelist' => array(),
                'blacklist' => array('2001:db8::/48'),
            ),
        ),
    ),
);
```

and the client only has an IPv4 address, should the client gain access to the `/stats` resource? Today's implementation denies the client access with the above configuration. The code actually ends up trying to match the IPv4 address against the IPv6 CIDR, which does not make much sense.