The Observer A hit comedy career plus a Palme d’Or for straight acting should be enough for anyone. Not ex-Kevin and Perry star Kathy Burke. Now directing a new Sam Shepard play, she talks about demons, heroes and life as a ‘smoking humanist’ Three years ago Kathy Burke began throwing plates. She turned over a few tables. ‘I called up a friend and just screamed down the phone at them,’ she says wide-eyed, as if surprised by the memory. There was, though, something familiar about this burst of anger. ‘I used to be terribly aggressive in my twenties,’ she says. ‘But I thought I’d sorted it out.’ Clearly she hadn’t.…