Feature/searchkick

Let me know if I should continue with [searchkick](https://github.com/ankane/searchkick), @jgrevich, but I got a little (and super basic) proof of concept going.

In short, searchkick provides a slick interface over ES which:

- stemming - tomatoes matches tomato
- special characters - jalapeno matches jalapeño
- extra whitespace - dishwasher matches dish washer
- misspellings - zuchini matches zucchini
- custom synonyms - qtip matches cotton swab
- similar items: https://github.com/ankane/searchkick#similar-items
- international languages https://github.com/ankane/searchkick#language
- and [more](https://github.com/ankane/searchkick/blob/master/README.md)!

This PR somewhat depends on https://github.com/18F/answers/pull/119, as I used the REPL to interact with ES. But, I can pull https://github.com/18F/answers/commit/b6198a1ccaa43a93bee5ec0c27e78d8672454ad4 out of this if you want.

To work with this locally, make sure you have ES running at port `9200`. Open a Rails console and type: `Article.reindex`.