Stuffing: Combine the prunes, raisins, and cider in a glass bowl, cover with wrap, and let soak overnight. Thinly slice the lemon and remove the seeds. Chop and saute the onion for 2 minutes in butter. Peel, core, and coarsely chop the apple. Coarsely chop the walnuts. Put the prunes, raisins, cider, and lemon slices in a saucepan, bring to a boil, reduce heat, and simmer for 10 minutes. Drain, chop finely, and place in a mixing bowl. Add all other stuffing ingredients, toss the dressing well, and taste for seasoning. Preheat the oven to 325 degrees. Goose: Salt and pepper the goose inside and out. Rub the sage thoroughly in the cavity. Stuff with the dressing and either truss or skewer the bird. Arrange the bacon slices over the breast, place the goose breast side up on a rack in a large roasting pan, and roast for 2 hours, pricking the skin with a fork and basting every 15-20 minutes. Remove the bacon, increase the oven temperature to 450 degrees, prick again with a fork, and continue roasting for 20 minutes or until golden brown. Transfer the goose to a large platter. Gravy: In a large saucepan, combine the neck and giblets (except the liver), water, onion, carrot, and celery, then bring to a boil. Add bay leaf and peppercorns. Reduce heat and simmer, skimming and discarding any foam, for 1 hour. Strain the stock through a fine mesh sieve into a medium bowl. Discard solids. Skim the fat from the pan juices, add 1 tablespoon or more of flour and stir until smooth. Slowly add 1 cup of the giblet stock, stirring constantly, bring the sauce to a boil, reduce heat, and continue cooking until gravy is thickened.