Use geoip.ubuntu.com/lookup for country/timezone lookup

The merits of this commit have been discussed in [#39](https://github.com/linuxmint/live-installer/pull/39#issuecomment-53173325). There are no drawbacks except relying on Ubuntu who might disable this URL at any time ([not really](https://launchpad.net/+search?field.text=geoip.ubuntu.com%2Flookup)), but you can always put up an alternative webservice serving GeoIP clues instead of showing IP only.