Languages: independent quality fields

**Is your feature request related to a problem? Please describe.**
The quality field is associated to a document, and the same for all language versions. This avoids featuring which is the main language (ie highest quality), that would have many usefull application.

**Describe the solution you'd like**
The quality field should be pushed in the locale, hence depend on the language.

**Applications**
- Add the quality logo next to the languages, when there is different languages. See e.g. https://www.camptocamp.org/routes/54424/.
- When the document does not exist in the language of the interface,
- suggest to create a version in the language of the interface in the language area
- choose a language to display with highest quality.

No files, tests, or entry points are named in the issue. Start by tracing how document quality and language versions are represented and rendered, then review the language area and the example route. Done means quality is independent per language and the interface supports the requested language suggestions and highest-quality selection.

Written by the indexing model from the issue text.