This commit makes Nodes special dicts that return None-like objects for
inexistent keys, making it a dynamic attribute store.
Also, it removes the D3MapBuilder and moves its logic to the Node and
Link classes' newly introduced export() method. Only they need to be
changed to populate the final nodes.json with more attributes.
Extending the visualisation data sources by the new batadv-vis,
which itself base ontop of alfred. Also extending the aliases import
by parsing informations from alfred. The last part is possible
through the preprocessing of data with alfred-json, so we don't
need to process the 'broken' format alfred itself supports.
This patch needs batadv-vis and tcatm/alfred-json in the PATH.
