For nearly four years, all viewers saw of lovely Muriel Young was something like this (see first pic) as she carried captions up to the TV cameras in programs like 'Rooftop Rendezvous" and 'TV Music Hall". Now she gets a chance of fame on a different screen - the cinema - in a new British drama 'Prison Story' with Jean Rice, Thora Hird and American star Beverley Michael. Muriel who is 26 and comes from Yorkshire, has only one regret. In the film she plays a 'first offender' and has been thorou