Canvas ND: use MapStructure for TFC, other misc.

Canvas ND: use MapStructure for TFC, other misc.

Implement traffic in MapStructure and use it. Various other hacks and/or
cleanup. Feedback required on whether this is a lot better than before.

Also partially revert 9c018d94c4d88dad7476ec250fa3b52024526f4b to add
feature to geo.PositionedSearch: it me._equals is overridden then the
old mechanism is used instead of the new C++ function, so that the
custom equality can be used. (In particular for the Fixes with the
TrafficModel class).