generateRailSignalConstraints.py: derive constraints for ordering bidirectional track use

[namdre]

• disposition needs a single constraint that encompasses the possibility of an order-swap
  • this implies that the outermost signals to a bidi-section must be found to avoid redundant constraints
• potentially the logic for traci.trafficlight.swapConstraints must be adapted (in this case we probably require a new constraint type)

Algorithm outline:

The following situation (structurally corresponding to a mergingSwitch) must be identified

• routes A and B share different directions of a sequence of bidi-edge-pairs x0,x1,x2,...,xn (reverse is -xn,..,-x2,-x1-x0)
• entry signal for A is first signal before x0
• entry signal for B is first signal before -xn
• ordering is based on arrival/started time at the first stop after the bidi-sequence

[namdre]

Open issue: if the next stop after the bidi section is on another ocp (much further away) compared to the point where the foe vehicle enters the bidi section, the the arrival-timing must take the travel time into account or the ordering is wrong.