Import new Autoupdater from joka

  If we change i.e. the mesh protocol or something else which
  breakes connectivity from mesh only nodes to their neighbours,
  they could get disconnected from the rest of the network.
  Therfore we try to update via the mesh network and if this fails,
  we try to find any open network to get our new firmware.

  This is also discussed in https://github.com/freifunk-gluon/gluon/issues/427