Support for Grafana 1.6.x + more than one datasource (graphite, influxdb, opentsdb...)

User can choose to get grafana from git or from an official release
User can choose its nginx install recipe
Delete the default nginx conf if it exists (when installing from rpm on centos for instance)
User can specify more than one datasource (graphite, influxdb, opentsdb...)
Bumped the version to 0.2.0 btw