Throughout 2013, London's Southbank Centre hosts a year-long music festival of 20th century classical music that takes as its starting point Alex Ross's book The Rest Is Noise. Laura Barton investigates the festival's first theme - Here Comes the 20th Century - and hears from the Southbank Centre's head of classical music, Gillian Moore, and London Philharmonic Orchestra's principal conductor Vladimir Jurowski about the opening all-Strauss concert on 19 January at the Royal Festival Hall