Raptor: Freq vj

Split vehicle journeys in 2 different subclasses:

* DiscreteVehicleJourney

  the 'classic' vj
* FrequencyVehicleJourney

  the frequency vj with start, end and headway as additional informations

This has been done:
* to reduce the size of the VJ (we removed 3 useless fields for DiscreteVJ, the most used kind of VJ)
* to reduce the size of the departure/arrival raptor structures (we now only store discreteVJ stoptime, no frequencyVJ stoptime)
* to better handle frequencies (there was some bug in the way frequencies were handled)

The 2 kind of VJ are handled 2 different way in raptor (in best_stop_time to be precise):
* DiscreteVJ are handled as usual with a departure/arrival sorted vector on which we loop through to find the best stop time (seenext_valid_discrete_pick_up /previous_valid_discrete_drop_off)
* FrequencyVJ are handled for the moment in a naive way

   We loop through all the jpp's vj to find the next one.
   We can use more clever data structure if needed

Je crois que le commentaire n'est plus d'actualité depuis que les stop_time sont des objects dans des vecteurs