Prioritize "direct" routes over transfers in group-filters

[t2gran]

For longer journeys taking a local train to save a few minutes and catch the night-train on the next station is not optimal. But, increasing the transferCost will have an unwanted effect on shorter trips.

Observed behavior

By turning the debug filter on we see that the direct alternative is lost:

The direct "night-train" alternative have the highest cost du to leaving 10 minutes before the 2 local train alternatives.

Version of OTP used (exact commit hash or JAR name)

dev-2.x

Data sets in use (links to GTFS and OSM PBF files)

Entur

[t2gran]

The current implementation of this have a bug. The cost calculation fails in some cases, e.g. if an itinerary do not have a walk access.

When testing this we also noticed that it would be easier to understand and work with this if this functionality is extracted from the group-by-filters and made a separate filter that just add an extra cost to the itinerary generalized-cost.