Update Elastic mappings to support search and aggregations

[delsborg]

The current mappings have most fields set to "string".
We should examine the use of keywords, text, and other analyzers for the fields.
A robust mapping should allow for use cases like:

1. Case insensitive search
2. Search on phrases
3. Accurate bucketing of terms
   . "Climate Change" = "climate change" -- both phrases should be in the same bucket

This would be a structure like:

{
  "mappings": {
    "_doc": {
      "properties": {
        "my_field": { 
          "type": "text",
          "fields": {
            "keyword": { 
              "type": "keyword"
            }
          }
        }
      }
    }
  }
}```

This would allow queries on my_field or my_field.keyword
It should also allow for more accurate bucketing of terms for aggregatons/facets.

This issue supports  #26
I created it to just address the specifics of the elastic mappings

Supporting documents: https://www.elastic.co/guide/en/elasticsearch/reference/current/fielddata.html
and  https://www.elastic.co/guide/en/elasticsearch/reference/current/analysis-analyzers.html