aligning stoptime stop_id/location_id/location_group_id && alternate_stop_name_exceptions.txt with spec

[CaylaSavitzky]

Summary:

according to spec: file - alternate_stop_name_exceptions.txt, fields - route_id && stop_id allow for non-numerical values in spec

file - location_groups.txt, field - location_group_name is an optional field

merge process was propagating stop_id value to location_id, & location_group_id (which are all supposed to be mutually exclusive)

• added test for this && added fix

Expected behavior:

Explain how you expect the pull request to work in your testing (in case other platforms/versions exhibit different behavior).

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