code: def get_all(self):
          
          res = self.es.search(index=self.index, doc_type=self.doc_type, body={'query': {'match_all': {}}})
          if not res['hits']['total']:
              return []
          return [Visualization.from_kibana(hit) for hit in res['hits']['hits']]
docs: Returns a list of all visualizations
          :return: list of the Visualization instances