Added: ssh proxy command support and additional parser arguments

In case your ffmap-backend server is not part of the mesh you can use
ssh to tunnel to your batman mesh:

  bat2nodes.py -m bat0 -s root@10.0.0.1 -d ../ffmap-d3 -n

Additional: support for dhcp.leases file (for aliases) and possiblity
            to skip rrd database.