Finalize languages (generic vocabulary)

[lnielsen]

• [x] Finalise the REST API /api/vocabularies/langauges
• [x] Finalise the integration of languages into the REST API /api/records.
• [x] Validate stored records should use meaningful ids (eng).
• [x] Validate indexed records.
• [ ] Update metadata reference documentation and REST API documentation
• [ ] Missing to index @v in denormalised records.
• [ ] Missing to redo the language facet.
• [ ] Missing to import the ISO language vocabulary.
• [ ] Postpone? Create language records with only needed languages (defined by BABEL_DEFAULT_LOCALE and I18N_LANGUAGES)

[lnielsen]

Remember to open an issue to verify UI after changes have been done.