Updated to GeoIP2

I not only modernized the API used and refreshed the GeoIP database, but also reduced the IO load by parsing the file only once as suggested by https://github.com/maxmind/GeoIP2-dotnet#database-usage which will a nice performance win with the current up to 100 games on the server list now that we are popular. Also added some try/catch for unforeseeable problems like https://github.com/OpenRA/OpenRA/issues/4601

Tip: Run with `Debug.IgnoreVersionMismatch=true` to see all games in the server browser.

The update to .NET 4.0 was required, because everything below is unsupported by the dependencies. Fetched the DLLs from https://www.nuget.org/packages/MaxMind.GeoIP2/