graphite: fix carbonCache graphiteWeb graphiteApi

This commit implements the changes necessary to start up a graphite carbon Cache
with twisted and start the corresponding graphiteWeb service.
Dependencies need to be included via python buildEnv to include all recursive
implicit dependencies.

Additionally cairo is a requirement of graphiteWeb and pycairo is not a standard
python package (buildPythonPackage) and therefore cannot be included via
buildEnv. It also needs cairo in the Library PATH.