Fix London bus stop app

[dinosaursrarr]

Looks like TfL have changed their response format. It used to provide details of the stop in the children attribute. Now, the relevant fields have been moved up to top-level fields, which is simpler.

Also being more tolerant of unknown bus stop letter codes.

Tested around my house (handful of top-level stops) and around King's Cross (many stops, nested within a hub).

Fixes https://github.com/tidbyt/community/issues/2656

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