'Sculpture has changed more in the last hundred years,' says Alastair Sooke, 'than in the previous thirty thousand.' The third and last episode of the series tells the dramatic story of a century of innovation, scandal, shock and creativity.     Romancing the Stone – The Golden Ages of British Sculpture episode 3   It begins with the moment at the turn of the 20th century when young sculptors ceased visiting the Elgin Marbles at the British Museum and looked…