You may love raindrops on roses, whiskers on kittens, glorious Alpine vistas and the smoldering passion of Christopher Plummer as Captain von Trapp — but how can you tell how much you really love them until you see them on the big screen? You can find out this Saturday.That's because, for one night only, The Sound of Music is playing in one of the most glorious theaters of all —Powell Hall, the longtime home of the St. Louis Symphony (718 N. Grand Boulevard).…