Add a new ISO 3166 code to country name mapping table

Summary:
This finally replaces the last aspect of the outdated and extremely slow
to parse countrytransl.map, and now uses the strings from the iso-codes
package that we also use for country name translations.

Reviewers: mlaurent, pino

Reviewed By: mlaurent

Subscribers: pino, mlaurent, svuorela, kde-pim

Tags: KDE PIM

Differential Revision: https://phabricator.kde.org/D15173