Grafana datasource and dashboard provisioning, initial versions (#532)

*  Grafana datasource and dashboard provisioning

 - Datasource (Prometheus) definition for docker network
 - Local and global dashboard stored as JSON in repo

Warning: If you make change to the datasources or dashboards in
Grafana UI and save them (to grafana.db), these definitions will
be overwritten upon start.
Export dashboards as JSON and update their files!

*  Update grafana dashboard