In the past week we were treated to not one, not two, but three sci-fi depictions of Herman Melville’s “Moby Dick” on television: Thursday brought us Leela’s obsession with a fourth-dimensional space whale on Comedy Central’s “Futurama”; Friday saw Cartoon Network’s “Thundercats” heroes at the mercy of a ship captain obsessed with destroying a tentacled beast called the Ramlak; and Saturday showed us Danny Glover as a version of Capt. Ahab hunting for the great white dragon that killed his family in the Syfy movie “Age of the Dragons.”