Jim Ferenczi 4682fc34ae Add the ability to disable the retrieval of the stored fields entirely
This change adds a special field named _none_ that allows to disable the retrieval of the stored fields in a search request or in a TopHitsAggregation.

To completely disable stored fields retrieval (including disabling metadata fields retrieval such as _id or _type) use _none_ like this:

````
POST _search
{
   "stored_fields": "_none_"
}
````
2016-08-24 16:40:08 +02:00
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