Feature: Slider in any directions. (#468)

Add the `SliderOption` option supporting:
```cpp
{
  Ref<T> value;
  ConstRef<T> min = T(0);
  ConstRef<T> max = T(100);
  ConstRef<T> increment = (max() - min()) / 20;
  GaugeDirection direction = GaugeDirection::Right;
  Color color_active = Color::White;
  Color color_inactive = Color::GrayDark;
};
```

In particular, this supports multiple direction. This resolves:
https://github.com/ArthurSonzogni/FTXUI/issues/467

This one do not support adding a label. The old constructors can still
be used to have a label.

src/ftxui/screen/screen.cpp

@@ -55,7 +55,7 @@ void UpdatePixelStyle(std::stringstream& ss,
   if (next == previous) {
     return;
   }
-  
+
   if ((!next.bold && previous.bold) ||  //
       (!next.dim && previous.dim)) {
     ss << "\x1B[22m";  // BOLD_RESET and DIM_RESET