Support updating trip wheelchair accessiblity information via gtfs-rt
Keep track of update seen in the gtfs-rt feed
Don't run StoptimeUpdater in an infinite loop

the PeriodicGraphUpdate should take care of running it as needed
Add ADDED trips to the TransitIndex

Existing RouteVariants aren't used: a new variant is created for each
trip.

+ store TableTripPatterns in the index
+ add methods to add/remove GTFSPatternHpFactore.Result from the index
Return null on a non-200 http response
Store stopsSequences in TripTimes
Add simple support for stoptime updates with delays
Add simple tests for StopTimeUpdater
Fix StoptimeUpdateTest
StoptimeUpdate: fix logging the number of applied updates
PeriodicGraphUpdater: catch updater exceptions
Stoptime Updates: Add TripTimes.State to store the source/status
gtfs-rt: avoid null value if feed failed to fetch
TransitIndex - basic computation of Stop#direction