Use Elasticsearch aggregations to calculate features

[ahalterman]

Right now, Mordecai calculates features like the number of results per country or the result with the most alternative names from the first 50 results that come back from the search. This isn't ideal, because it involves bringing all 50 results back, which is inefficient, and allows us to only look at the top 50.

Instead, use ES's aggregations to calculate that stuff directly on the server. I have this working for the number of results per country, but calculating the number of alternative names will require modifying the index to include that information.

Most importantly, making these changes will requires retraining the model since the values of the features will be different (and hopefully better).