add space perf. numbers
add metrics-copier, which copies all metrics from mysql to elasticsearch
store metrics into elasticsearch instead of mysql

* elasticsearch seems to perform much better to retrieve metrics,
  mysql queries would become complex and slow and take minutes.
  (see experience with graph-explorer's structured_metrics)
* the implementation is more elegant (both storing and querying),
  and actually seems to perform better for storing as well
* elasticsearch is also easier to install/run
* this means metrics-copier isn't needed anymore