Increase facet size to a big-enough number

Looks like due to https://github.com/elasticsearch/elasticsearch/issues/1776 we cannot make the size unlimited, but that might be a bad idea anyhow.

Caveat: I wrote this based only on http://www.elasticsearch.org/guide/reference/api/search/facets/terms-facet/

If this does not work as expected, should be easy to sort out.