Fernando? Dancing Queen? SOS?  Welcome to the megarate on ABBA's Greastest Hit album 'Gold: Greatest Hits'. Which GOLD hit will win the winner title?  Anyone looking for the key to Abba's enduring appeal should look no further than "Voulez Vous" and "Gimme! Gimme! Gimme! (A Man After Midnight)" for their answer. There was an innocence to the Swedish quartet, even when they were singing about one-night stands and the invitations to them. Gold establishes that the band, while appre