Young Vic, LondonThe discovery of what could be a painting by Hitler leads to a moral quagmire in Patrick Marber's punchy staging of Marius von Mayenburg's play Arrive early, and you'll see the cast tidy a load of junk: Nicola and Philipp are sorting their dead dad's stuff. When the play begins, the stage is clear " except for a watercolour stashed in the attic. It's a tame sepia view of a church with a signature tha…