Refactor batctl calls into python class.

This drastically reduces the logic implement in mkmap.sh and also
supports multiple batman mesh interfaces.
Additional argument for batctl binary.

Without using the tool in an PATHless enviroment fails.
Fix utf-8 enforcing hack.

The function getdefaultlocale takes one argument, so the replacing
lambda function should also.
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.
Beautify node stats.

Also display both rrdb fields in one graph.