Allow Design Properties optionally true by default.

When styling widgets it may not suit to override existing classes, and rather use custom classes. Creating a “default” style for widgets in Design Properties which can be opt-out rather that opt-in would make sense and result in less custom CSS requiring more overrides when the default styling is unwanted.

"SomeWidget": [
      {
        "name": "Default Style",
        "type": "Toggle",
        "description": "Default style.",
        "class": "my-custom-some-widget",
        "default": "true"
      }
    ]