Added configuration option to change the location of the .dat-File

Hi,

Thanx for this bundle! Very nice!

As have my Web-App in a shared-environment, I added the option to configure the file-path where the Geo*.dat-File is located, so I only have to maintain one GeoIP-Database for the environment, instead of one for every application.

The change is fully backwards compatible, as the file path defaults to the same value as before the change.

I also added phpUnit-Tests for this option.

Please let me know if you intend to merge this pull-request into your bundle or if I should keep my fork.

Best regards,
Dominik