Create `features/dui` package

[yohamta]

• [ ] Create dui package
• [ ] Create Style component for layout options
• [ ] Create a Flexbox layout engine based on ECS architecture (from scratch or migrate code from furex to cut corners)
• [ ] Ability to add child entities

dui.Create(ui.Config{
  Style: {
    // .. style options
    Top: 100,
    Left: 100,
    Width: 300,
    Height: 300,
  },
}).WithChildren(
  ui.Create(ui.Config{
    Style: {
      // .. style options
    },
  },
))