Theatre Royal Stratford East, LondonJonathan Harvey's breakthrough play still blazes with a stubborn utopian impulse thanks to finely pitched performances and delicately balanced banter Everyone lives cheek by jowl on this south London estate, but there's still space for secrets. In Rosie Elnile's smart design, the walkway sits bang at the front of the stage: we're properly involved in this 30th anniversary revival o…