OpenData/GBFS Bike Rental Updater

[jmfield2]

Currently, the opendata updater has some issues:

• [ ] The output XML parent node matches the leaves (stations/stations) where it should probably be stations/station.
• [ ] It would be nice to separate the hubs from the bikes either via another API endpoint, or as stations vs. bikes lists in the XML output.
• [ ] Improve/test the way hubs are loaded (via two hits to the upstream API each update)
• [ ] Add GBFS auto-discovery support

Note that some of these may require upstream discussion with OpenTripPlanner developers unless the code can be split into a separate class or interface without breaking the other bike rental updaters.

Also, we should be certain of any changes to the bike rental routing code.

[barbeau]

Note that GBFS support now exists in the OTP master branch (via PR https://github.com/opentripplanner/OpenTripPlanner/pull/2458), so any of these changes should be based on the upstream OTP project.

We should also update our branch to use the upstream branch, instead of our own implementation, and add any new features that our GBFS implementation has but are missing in main OTP project as PRs to the new OTP project. For example, our GBFS implementation has two separate updaters for floating bikes and hubs, and we discovered that this is more fault tolerant, as one updater can fail due to 404 and the other keeps working. The main OTP branch failed on a 404 from the floating bike API, which took down the hub updates as well.