Implement exit_country behaviour.

[svaningelgem]

I wanted to see if it's possible to specify an exit country (like you can do in the torrc file).
In this PR you'll find one possible implementation.

[SaiKiru]

For those wanting to try this out, when using the latest version for location_ipfire_db_reader, remove line 475 from consesus.py as the download() method is no longer necessary nor included, and will result in an error.

[svaningelgem]

Thanks for the tip @SaiKiru , I adjusted the code as you suggested.