Consider tighter limit on car linking

[ansoncfit]

The construction of stopToPointLinkageCostTables now uses mode-specific limits, rather than the constant 2km distance table limit.

In LinkedPointSet, CAR_TIME_LINKING_LIMIT_SECONDS = 30 * 60 and MAX_CAR_SPEED_METERS_PER_SECOND = 44 (~160 km / hr). The time should be an upper bound on a user-definable maxCarTime parameter in the UI, and the speed should be an upper limit on car speeds from OSM.

But an ~80 km distance table radius may be excessive -- for Los Angeles, building car linkage cost tables for this radius takes ~2.5 hours. Once we serialize non-walk linkages, a long build time will be less onerous (as it will only be done once). But in the meantime, and maybe even long-term, we may want a lower limit.

[ansoncfit]

Another reason for lowering the limit: times for the initial access leg come from a street router, not pre-computed tables, so the initial access leg can exceed the hard-coded R5 limits.

[ansoncfit]

For the example we discussed in Switzerland, in which the time to build stop to point linkage cost tables was not excessive, weren't the stops limited to a couple thousand rail stations?

To allow building stop to point linkage cost tables for car egress and many thousands of transit stops, I think a distance limit of 45 km (30 min at 90 km/hr) would be sufficient for the vast majority of use cases. If anyone needed a higher limit, we could make a custom R5 version.