Extend net2geojson.py to optionally include numLanes and speed as properties

[RobertHilbrich]

Geometries in GeoJSON format of a SUMO network are sometimes used in web-based applications (e.g. SESAM or Baustellenatlas) based on OpenLayers or Leaflet. It would be great to include the following additional properties for an edge (or lane) as part of the GeoJSON input:

• Number of lanes
• Speed limit
• Maybe: allow/disallow status

These properties should be optional to avoid inflating the resulting file if they are not needed.

Tricky: what if lane geometries are rendered, but we want to include edge properties (e.g., number of lanes).