Fix "fields" annotation

[wasinger]

The fields property inside the Property annotation did not work. Though the Property class already had the fields member this was unused and one had to write the fields mapping inside the settings array. Now the following annotation works correctly:

    /**
     * @ES\Property(
     *  type="text",
     *  fields={
     *    "raw"={"type"="keyword"},
     *    "increment"={"type"="text", "analyzer"="incrementalAnalyzer"}
     *  }
     * )
     */