- Massage the implementation a bit, don't insert a meaningless
copy of the key as the untranslated message.
- Add isEmpty() to check for presence of the untranslated message.
- Document API.
- Update tests.
- While QObject::tr and gettext give us translations **most** of the
time via the translation mechanism, we sometimes have strings
embedded in configuration files that need to be shown to people
as well. Follow the .desktop style in handling this.
- A key's value **might** be translated; use `key[lang]` for the
translation into one of the languages that Calamares understands.
Code that expects a translated (human-readable) string in a configuration
file can use TranslatedString to collect all the translations of a
given key, so that it displays the right string from the configuration
when needed.
