Not all the heroes with superpowers are on the big screen in Marvel’s “Avengers: Age of Ultron,” the year’s most anticipated movie that opened in theaters this month. Some are behind the screen. Earlier at the cast and crew screening held at the Academy of Motion Picture Arts and Sciences, Los Angeles, four young adults with autism from Exceptional Minds Studio were singled out by Marvel Studios’ Executive VP of Visual Effects and Post Production Victoria Alonso for their work…