Facet values linked to taxonomies should be translated using the taxonomy

[alexgarel]

What

• We currently display facets value as the normalized value, while we should display the translated value.
• Facet values linked to taxonomies should be translated using the taxonomy

Part of

• 🎯 What can I work on ? (search-a-licious) #62

[alexgarel]

I see two way to do that:

1. simply keep a dict in memory that maps values to translation in the different languages
2. use a key value database like leveldb or equivalent and update it on each taxonomy changes

First option might be memory consuming, and could take time to start-up.
Second option is nearly as fast, more efficient in memory and do not consume time at startup, but adds a dependency.

I considered the option to generate po files when we import taxonomies and use Babel to translate, but Babel is not memory efficient at all !

[alexgarel]

Finally there is even simpler: using ES in one query to get all translated values.