Add destination directory argument and write content instead of piping.
Generate node stats with rrd.

We have an rrd for every active node. On every run we update
stats about client count and node state from nodes.json to the rrd
databases. After updating the rrds we are able to generate a stat
graph (image) for every node.

The rrds are stored in subdirectory "nodedb" of the scripts location and
the generated images in subdirectory "nodes" of the destination directory.
Both directorys must exist bevor starting the script.
Fix link handling.

Accidental the LinkConnector object was used for checking the nodes,
this patch fixes this behaviour.
Beautify node stats.

Also display both rrdb fields in one graph.
Reduce clientCounter for every node.

We have an ghost client for every node, we don't want them in the global
client measurement.
Merge branch 'rrdstats' of https://github.com/toppoint/ffmap-backend into toppoint-rrdstats

Conflicts:
	bat2nodes.py
	mkmap.sh
Merge branch 'toppoint-rrdstats'