Convert More Like This searches from API endpoint to query

Elasticsearch 1.3.0 introduced the addition of IDs to the [More Like This query](http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/query-dsl-mlt-query.html). This allows much more flexibility than the API endpoint as changes in 1.3.0 allow the query to behave much the same as the API endpoint if we want to use it that way.