Mix the gelatin, half of the sugar and the salt in a saucepan.In another pan, beat the egg yolks well.Add the lime juice and water to the egg yolk mixture.Stir the egg yolk mixture into the gelatin mixture.Cook over low heat, stirring constantly, just until the mixture comes to a boil.Remove from heat;stir in grated peel.Chill, stirring occasionally, until the mixture mounds slightly when dropped from a spoon. Beat the egg whites until soft peaks form.Gradually, add the remaining sugar, beating until stiff.Fold into the chilled gelatin mixture.Fold in whipped cream (reserve some for topping, if desired).Pour into the baked crust.Chill until firm.