Take Geolocation of IP addresses into account for account approval

Pitch

It would be great for our admin process if:

1. Geolocation could be shown in the account moderation interface next to the IP addresses, either built-in or even just as a link to a service that will show it.
2. Geolocation could be included in IP address rules - we would quite like to auto-reject anything that doesn't geolocate to the UK.

Motivation

As with everyone else, we've got loads of spambots at the moment. In order to separate out the real and fake accounts, as we're a UK-specific instance, we look at IP geolocation to as part of that moderation decision. At the moment that involves copy/pasting into a service like http://whatismyipaddress.com, but that's a faff and we don't always remember to check every single one.

This will presumably involve talking to an external service, so it should of course be opt-in because data gets sent elsewhere.

I'm sure there's plenty of wider issues to consider with this, but it would certainly make our admin lives easier.

See also #40714 for a similar idea on email domain checking.