estatsd: add in stats app dependencies

- https://github.com/jsonified/estatsd for vm stats and custom metrics via Graphite
- forked from original https://github.com/RJ/estatsd.git
estatsd: implement metrics via graphite & estatsd
estatsd: control estatsd and graphite settings from _config and ini files
estatsd: read vm_name from app env, otherwise default to node()

- add `vm_name` parameter to environment, and store in state
- allows collecting uniquely named VM metrics even if epmd is not running