More robust, flexible handling of ip2cc determination

We should support multiple external solutions for IP to location mapping, while probably having a simple fallback like the one already implemented.

Existing Drupal modules handling ip2cc or similar functionality generally are uneven, are tied to their particular proprietary third party solutions, lump in a lot of additional functionality, and produce data in very different ways.

As in many other cases, e.g. wysiwyg, there's a need here for a generic API that can be used for various third party solutions, providing data in an established format.

This needs to be done. For high traffic sites we can't rely on an external service.

Proposed implementation:

1. Introduce a hook_country_code_handler through which modules can register their handlers for country code determination.

2. Implement this hook in country_code using the existing call.

function country_code_get_country_code_hostip($ip_address) {
  return strtolower(file_get_contents('http://api.hostip.info/country.php?ip=' . $ip_address));
}

function country_code_country_code_handler() {
  return array(
    array(
      'name' => t('hostip.info'),
      'country_code_get_country_code_hostip',
    ),
  );
}

3. Introduce an admin setting to select which handler to use.

4. Write implementations for other, more robust handlers.

I'm going to implement this approach.

Introduced this hook with the existing hostip implementation.

Added a config option that shows up only if there is more than one hanlder available.