Find the way to simplify rebuilding UI from the next model

[shamansir]

Now it's like this, in update

        ToExample dmsg ->
            (
                if ExampleGui.updatedBy dmsg then
                    let nextModel = example |> Example.update dmsg
                    in
                        ( nextModel
                        , gui
                            |> Tron.over
                                (ExampleGui.for nextModel |> Builder.map ToExample)
                        )
                else
                    ( example |> Example.update dmsg
                    , gui
                    )
            , Cmd.none
            )