Be able edit (in case of database repo) translations in phrases page

[oriolbcn]

Ideally we need to make the updates via AJAX from Vue. In order to do that we need to support the JSON format in the update method and return the updated translation. Also see if we can get the csfr token.

From Vue we make the request and update the translation in the front-end too. We can add the path to call for each translation when rendering the template from Rails, and probably also the authenticity token to pass the csfr protection (otherwise we would need to disable it for this endpoint)