“Can theatre and rock music ever mix? It’s a question that rears its poodle-haired head every few years or so. Whether the answer is to be found in anything other than a greatest-hits medley hung on a paint-by-numbers plot is another matter. The new play this time is Nevermind, a fringe piece at the Old Red Lion Theatre in Islington, North London about a manic depressive music journalist visited by the ghost of Kurt Cobain.”