Allow changing of bogons update frequency

As concerns have been raised with the update duration of the fullbogons lists in the forum [1], I have added an option to increase the update frequency. It does not change the default update frequency such as not to increase the required bandwidth too much.

I also intend to add further options such as support for compressed lists and custom urls which should again decrease the required bandwidth.

[1]: http://forum.pfsense.org/index.php/topic,57286.0.html