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.