create a filtered query if there are filters set

Change _normalizeQuery to create a filtered query if the queryObj has filters.  For example:

    "query": {
      "filtered": {
        "filter": {
          "and": [
            {
              "term": {
                "tag": "Seasonal"
              }
            }
          ]
        },
        "query": {
          "query_string": {
            "query": "food"
          }
        }
      }
    }