We can't use the same class to map ISO 3166-1 and CGSpace country
vocabularies because our Gson is old and lacks the support for the
"alternate" value in its annotations (added in Gson 2.5). So it's
better to create multiple classes that extend the base one instead
of creating a custom deserializer. Each extended class then uses
its own Serializedname.
If an item has country metadata (cg.coverage.country) and no alpha
codes we check for name matches in ISO 3166 and add alpha_2 codes.
The name matching checks for a case-insensitive match on either an
ISO 3166-1 name, official name, or common name.
Our Java class needs to match the input JSON structure exactly, but
we can't use "3166-1" as a variable name so we tell GSON to use the
name "3166-1" when deserializing to countries.