query: #by Jura1, 2016-01-24
  
  SELECT ?extension (COUNT(DISTINCT(?filename)) AS ?count) WHERE
  {
    ?item wdt:P1621 ?filename .
      BIND(fn:lower-case(REPLACE(str(?filename), '(.+?).(\u005B^.\u005D*$)', "$2")) AS ?extension)
  }
  GROUP BY ?extension
  ORDER BY DESC(?count)
  LIMIT 10