DATAMONGO-952 - Derived query should consider @Query(fields=…

We check for the presence of field restrictions in the way of single string field name or as json representation in form of `{ fieldname : 1 }` and apply those to the derived query. 

Therefore we moved parameter replacement from `StringBasedMongoQuery` to `PartTreeMongoQuery`.

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Should be back ported to `1.5.x`
This one does (though not clean) also applies on `1.4.x`.