Better docu how to checkout git submodules
use nix 2014.04 release instead of unstable
install policycompass-services, work in progress
use stable nix channel 2014.04 instead of unstable

This way we have less updates.

This brakes the pyflake package, so this is removed.
readded pep8 and pyflakes
Fix: the supervisor download link is not stable, use git instead
add mockserver for adhocracy auth