Add controls to the ActorToolbox in the GUI tab. Add dragging and dropping controls from toolbox into scene and prefab trees.

Source/Engine/UI/GUI/Panels/GridPanel.cs

@@ -8,6 +8,7 @@ namespace FlaxEngine.GUI
     /// A panel that divides up available space between all of its children.
     /// </summary>
     /// <seealso cref="FlaxEngine.GUI.ContainerControl" />
+    [ActorToolbox("GUI")]
     public class GridPanel : ContainerControl
     {
         private Margin _slotPadding;