route, graphHopper: Use generic turn instruction codes

Merged Marcus Lundblad requested to merge wip/mlundblad/additional-turn-icons into master

Makes the generic query points use codes independent from the GraphHopper API codes. This avoids mixing GraphHopper-related codes with extra codes for instructions such as elevators used by OpenTripPlanner. Also properly handle U-turn instructions from GraphHopper so that they get appropriate icon.

Implements #402 (closed)

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