Claude Cahun is the most important artist you've never heard of - until now. Writer, photographer, lesbian; revolutionary activist, surrealist, resistance fighter - Cahun witnessed the birth of the Paris avant-garde, lived through two World Wars and, as "Der Soldat ohne Namen", risked death by inciting mutiny on Nazi-occupied Jersey. And yet, she's until recently been merely a peripheral figure in these world-shaping events, relegated by academics to the footnotes in the history of art, se...