bug 839214 - elasticutils and search mapping

This only sets up an initial index - we will make more changes and tweaks as we make it power the search interface.

To spot-check:

1. `vagrant provision` to install the new [elasticsearch-head plugin](http://mobz.github.com/elasticsearch-head/) to the vm.
2. Go to https://developer-local.allizom.org/elastic/_plugin/head/ to see an empty ES cluster.
3. `manage.py cron reindex_documents`
4. Should see a PUT line output for each doc in your vm
5. Refresh https://developer-local.allizom.org/elastic/_plugin/head/ to verify the docs were successfully added to the ES index