allow transfer between walking and taxi at parkingAreas

[namdre]

1. --persontrip.transfer.walk-taxi parkingAreas (works like ptStops but with additional locations)
2. --persontrip.transfer.walk-taxi occupiedParkingAreas (only uses a parkingArea if a taxi of the appropriate line is already parked there

Also: --persontrip.transfer.taxi-walk parkingAreas

When a taxi trip ends at a parkingArea, the taxi should park there (and occupy a spot)

One of the use-cases for occupiedParkingAreas would be a car- or bike-sharing service where the user picks up a parked shared vehicle and leaves it at a designated place.

There are several implications of using such a dynamic routing scheme as occupiedParkingAreas:

• availability of vehicles must be drawn from the current simulation state
  • this mail fail for long-range routes where the person arrives at the parkingArea in the far future
• when passing the same inputs to duarouter, surrogate information must be taken
  • i.e. assume avaiability of vehicles at all stations
  • load some time dependent availability state from a prior simulation run (thus allowing for iterative assignment)