Change the way config and heads are downloaded

The review-planet-config-heads script downloads the planet-config file and the files from planet-heads directory and compares them with the same files in the planet-git repository. Earlier only Debian members could run this script (ones who have access to the lw08.debian.org). Now it downloads data from the deriv.debian.net and can be run by everyone.

I experienced some problems while trying to download the heads from the deriv.debian.net. The solution was found here: https://serverfault.com/questions/462021/problems-with-wget-aws-ubuntu-apache2