Includes the following changes of Zsombors commit: Add basic support for ADDED trips.
* add getAllStops(), getAllRoutes() to TransitIndexService
* modify Updates to store an AgencyAndId for stops
* handle different updates in separate functions in StoptimeUpdater
Adding trips is not included in this commit.
Process incoming update messages atomically. Incoming requests either
see all updates of a message or no updates of a message.