Fix associating to Taric country groups in ChiefTransformer

For countries we have been using Chief::CountryCode.to_taric to get
TARIC equivalent of CHIEF country code. This adds similar functionality
to Chief::CountryGroup and maps groups as well.
Add national country group names to initial seed file
Add data migration for fixing national country group names
Rename data migration to follow naming convention with timestamp

No impact on data, just a rename
Fix national Certificate description

Happened due to mass rename in static_national_data_insert.sql when
moving to point in time architecture
Fix validity period of national certificate type

This was a result of certificate type description being blank as
validity period is part of the query of time machine
Merge pull request #105 from alphagov/55706190-invalid-country-group-and-description-on-measure

55706190 invalid country group and description on measure