sub folder for element containers + horizontal panel + shorthands for horizontal and vertical panel

Source/Editor/CustomEditors/Elements/Container/SpaceElement.cs

@@ -0,0 +1,30 @@
+// Copyright (c) 2012-2021 Wojciech Figat. All rights reserved.
+
+using FlaxEngine.GUI;
+
+namespace FlaxEditor.CustomEditors.Elements
+{
+    /// <summary>
+    /// The spacer element.
+    /// </summary>
+    /// <seealso cref="FlaxEditor.CustomEditors.LayoutElementsContainer" />
+    public class SpaceElement : LayoutElementsContainer
+    {
+        /// <summary>
+        /// The spacer.
+        /// </summary>
+        public readonly Spacer Spacer = new Spacer(0, 0);
+
+        /// <summary>
+        /// Initializes the element.
+        /// </summary>
+        /// <param name="height">The height.</param>
+        public void Init(float height)
+        {
+            Spacer.Height = height;
+        }
+
+        /// <inheritdoc />
+        public override ContainerControl ContainerControl => Spacer;
+    }
+}