// TODO: AddArmorImpl, etc are small enough that they would probably better inline.
        private IObservable <ArmorViewModel> AddArmorImpl()
        {
            var armorVm = new ArmorViewModel();

            Armor.Add(armorVm);

            return(Observable.Return(armorVm));
        }
        private IObservable <ArmorViewModel> RemoveArmorImpl(ArmorViewModel armorVm)
        {
            Armor.Remove(armorVm);

            return(Observable.Return(armorVm));
        }