It's 40 years since the National Theatre was led by someone who wasn't a Cambridge graduate, but this week it was announced that Rufus Norris - who spent his late teens as a painter and decorator - would succeed Sir Nicholas Hytner as the theatre's director. So why is Norris such a popular choice for British theatre's top job? Mary Ann Sieghart looks at the making of a director whose work includes collaborations with Damon Albarn and the London Community Gospel Choir and a musical about a real-life serial killer.