LONDON -- The Royal Ballet, unlike some of its peers (hello, Paris Opera Ballet), isn't known for extensive forays into contemporary European dance. But on Thursday night, a double bill that included the commission of a new work, "Salle de Danse," by Paul Lightfoot and Sol León -- well-known names on what the English still like to call "the continent" -- opened at the Royal Opera House to a buzzy crowd. Lightfoot and León occupy an interesting corner of the dance landscape.