* how to handle NaN values form batch importer like flumotion-rrd?
* should we allow floats for client-count, bytes-sent etc.?
* address issues with python-twisted dropping messages when transmit
  buffer is full
* move common code of python-twisted based importer to seperate module
* fix wrong usage of twisted
* hub: implement foward-only mode (delete dataupdates from local store
  as soon as they are forwareded)
* hub: add geo-ip lookups
* hub: add support for Elasticsearch 5.x
* hub: add additional checks at protocol parser
* hub: sanity check len(clients) and clients field in date update (as well as bytes-sent/received)