Makesnippetqueryrelevant: display snippet showing the area surrounding the searched word / phrase text

Added the cosine similarity as an addition factor with weight.

To get the query term in the snippet. Attached is the image from local testing.

Most of the document seems to get the query word but few of them are still not able to get the query words, but snippet is picked from a location very close to the query word. needs a little more tunning of parameters for that i guess.

![2014-08-28-16 37 44-screenshot](https://cloud.githubusercontent.com/assets/1573133/4074644/e778e1a6-2ea3-11e4-94e6-9ed9f91c7fcc.png)

The query string might have operators, prefixes, boolean filters, etc in - e.g. for `subject:(stemming OR lemmatisation)` we don't want to base the snippet on where the text contains `subject` or `OR`.

I wonder if we'd be better to use `QueryParser` here, or maybe to pass in the parsed query.  Not sure what to do about the potentially different stemmer settings though.