Remove integration with Apache, serve a local service with gunicorn

This PR removes the dependency on puppetlabs-apache, for installations that would rather use nginx or another webserver to proxy to graphite. Instead, we install a `graphite-web` upstart job which uses gunicorn to run graphite-web on a local port.

This PR also makes the graphite installation directory configurable.

See the submitted commit message for more detail on the above.