Include all labels in subject index

[scuy]

In order to be able to implement auto-completion (#19) based on AAT concepts, all labels in all available languages have to be included in the subject index.

[eafiontzi]

Included in the aat index, for example:

{
            "_index": "aat",
            "_type": "terms",
            "_id": "300004062",
            "_score": 1,
            "_source": {
               "prefLabels": [
                  {
                     "label": "anexos",
                     "lang": "es"
                  },
                  {
                     "label": "bijgebouwen",
                     "lang": "nl"
                  },
                  {
                     "label": "annexes",
                     "lang": "en"
                  },
                  {
                     "label": "annex",
                     "lang": "en"
                  },
                  {
                     "label": "anexo",
                     "lang": "es"
                  },
                  {
                     "label": "bijgebouw",
                     "lang": "nl"
                  },
                  {
                     "label": "construcción",
                     "lang": "es"
                  }
               ],
               "prefLabel": "annexes",
               "providerMappings": [],
               "id": "300004062",
               "broader": [
                  {
                     "prefLabel": "building divisions",
                     "id": "300072553",
                     "uri": "http://vocab.getty.edu/aat/300072553"
                  }
               ],
               "uri": "http://vocab.getty.edu/aat/300004062",
               "altLabels": [],
               "scopeNote": "Subsidiary supplementary structures, whether additions to a main building or separate from it, but usually visibly distinct and often with a separate entrance."
            }
         },