Lyn Paul may have started her career off as a supporting child actress playing ball in front of the corner shop in the very first episode of Coronation Street, but she is most certainly the centre stage stalwart in Willy Russell's Blood Brothers.    The Winter Gardens Opera House played host to a diverse audience, with a noticeable sprinkling of students who were not necessarily bypassing BBC Bitesize, but seeking to go a peg better with the ultimate revision guide for GCSE English Lit.     So did you hear the story of the Johnstone twins ?  As like each…