TermVariants from fuzzy and/or span search

This is a request handler wrapper around components in ConcordanceSearcher submitted in LUCENE-5205. It quantifies the variation in term matches of a fuzzy search, and optionally returns group counts for other categorical fields or class values in a document.

It does do some distributed tf*idf calculations for fewer than 25 shards.

**Following Yonik's Law**
This is patch is more of a placeholder for a much more polished draft. Among other things, test scripts and javadocs are forthcoming!

A Lucene-based implementation is also forthcoming, see Tim Allison's code.