The story of Northern Songs did not end with the sale to Sir Lew Grade.      Over the years, it went through the hands of Robert Holmes A Court, Michael Jackson and the conglomerate worth more than two billion dollars now known as Sony/ATV.       How did Michael Jackson get involved, and how did the 1976 change in Copyright Law affect the way John Lennon (and later Yoko Ono and the estate), and now Paul McCartney approach the business of their publishing.    Find out this and more this week!