Check tables in each GTFS file and verify them

[CBROWN-ONS]

          I can think of 2 other conditions we would want to check for raise:

1. Fewer files than expected
2. Additional files than expected (perhaps a warning is more appropriate here if we can test it without having it show up in test reports)

As logic not implemented, this can be a feature request. Would you agree?

Originally posted by @r-leyshon in #112 (comment)

[CBROWN-ONS]

Discovery

It appears that gtfs-kit will only read in tables that are included the the following dictionary.

It will however not raise any errors or notifications, informing the user that it has not read this table, or that it even exists.

On the other hand, gtfs-kit will notify the user if one of the required tables are missing, This will appear in the table returned through feed.validation.

Recommendation

In this case, I recommend that we wait for the cleaners/validation modules to be merged with dev and then alert the user in the validation table of the invalid table that isn't being read as part of the GTFS feed.

[r-leyshon]

Migrated to datasciencecampus/assess_gtfs#7