allow creation and modification of vTypeDistributions (trac #2862)

[behrisch]

Migrated from http://sumo.dlr.de/ticket/2862

{
    "status": "new", 
    "changetime": "2017-02-13T12:51:26Z", 
    "description": "", 
    "reporter": "namdre", 
    "cc": "", 
    "resolution": "", 
    "_ts": "1486990286727655", 
    "component": "TraCI", 
    "summary": "allow creation and modification of vTypeDistributions", 
    "priority": "major", 
    "keywords": "", 
    "time": "2017-02-13T12:51:26Z", 
    "milestone": "1.0.0", 
    "owner": "", 
    "type": "enhancement"
}

[namdre]

MSVehicleControl::myVTypeToDist must be updated whenever distributions are added or modified (#2863, #4412)