Make i18n URI builder a parameter / a config element in config.json

[PonteIneptique]

In implementing arethusa_to_widget, it feels to me that

$translateProvider
       .useStaticFilesLoader({
+        prefix: 'http://localhost/widget/i18n/',
         suffix: '.json'
       })

should be overwrittable through config.json value so that I can pass it something built from my backend framework and not hardcode it in the backend framework.