meanData output should reported speed averaged over vehicles in tracking mode (trac #2873)

[behrisch]

currently, the speed is averaged over the samples. This gives greater weight to slow vehicles since they spend more time on the edge.

In tracking mode it is feasible (from an efficiency viewpoint) to also provide a vehicle-based average speed where all vehicles are weighted the same, similar to a point-based detector.

Migrated from http://sumo.dlr.de/ticket/2873

{
    "status": "new", 
    "changetime": "2017-02-16T12:36:12Z", 
    "description": "currently, the speed is averaged over the samples. This gives greater weight to slow vehicles since they spend more time on the edge. \n\nIn tracking mode it is feasible (from an efficiency viewpoint) to also provide a vehicle-based average speed where all vehicles are weighted the same, similar to a point-based detector.", 
    "reporter": "namdre", 
    "cc": "", 
    "resolution": "", 
    "_ts": "1487248572576534", 
    "component": "simulation data output", 
    "summary": "meanData output should reported speed averaged over vehicles in tracking mode", 
    "priority": "major", 
    "keywords": "", 
    "time": "2017-02-16T12:36:01Z", 
    "milestone": "1.1.0", 
    "owner": "", 
    "type": "enhancement"
}

[behrisch]

@namdre changed milestone from "" to "1.1.0"