Improve E045 - allow stop_sequence/stop_id mismatch if stop_id belongs to same station

[barbeau]

Summary:

As discussed in #297 - currently there is an undocumented use case for GTFS-RT where some consumers support real-time platform re-assignment by changing the stop_id in the TripUpdate. Some producers such as MBTA are producing this type of data.

Currently, E045 flags any case where the stop_id and stop_sequence do not match GTFS:
https://github.com/CUTR-at-USF/gtfs-realtime-validator/blob/master/RULES.md#E045

We should allow a mismatch without throwing an error if the original stop_id and the new stop_id belong to the same parent station. Otherwise, it should still be considered an error.

Steps to reproduce:

Run validator on MBTA TripUpdates feed:

• https://cdn.mbta.com/MBTA_GTFS.zip
• https://cdn.mbta.com/realtime/TripUpdates.pb

Expected behavior:

Don't throw E045 on platform changes

Observed behavior:

Eo45 is thrown on platform changes