National Portrait Gallery, London The actor’s life in pictures, from mousey-haired teen to American icon to her shocking death at 36, beams with the charm that defined a century. But why aren’t we shown more of what lay behind the smile? I wanted to hate the National Portrait Gallery’s new blockbuster show, Marilyn Monroe: A Portrait . It represents two things that really should be binned: anniversary exhibitions (it marks Monroe’s 100th birthday) and exhibitions of celebrity portraits. Annivers