Fixed 20010 - Missing locale and translation support in Twig & Public API, locale mapping needed

This PR addresses the locale and translation support issue by using a map between eZ Publish locales and POSIX locales which are used in Symfony.

The LocaleConverter works in both ways (from/to POSIX format)

## Tasks
- [x] Implement a LocaleConverter, configuration based.
- [ ] Add semantic configuration to be able to easily add custom locales to the map.