Added new NonDrawingGraphic control and editor script

Resolved request #107

--HG--
branch : develop_5.3

Editor/NonDrawingGraphicEditor.cs

@@ -0,0 +1,21 @@
+/// Credit Slipp Douglas Thompson 
+/// Sourced from - https://gist.github.com/capnslipp/349c18283f2fea316369
+/// 
+using UnityEditor;
+using UnityEditor.UI;
+
+namespace UnityEngine.UI.Extensions
+{
+    [CanEditMultipleObjects, CustomEditor(typeof(NonDrawingGraphic), false)]
+    public class NonDrawingGraphicEditor : GraphicEditor
+    {
+        public override void OnInspectorGUI()
+        {
+            base.serializedObject.Update();
+            EditorGUILayout.PropertyField(base.m_Script, new GUILayoutOption[0]);
+            // skipping AppearanceControlsGUI
+            base.RaycastControlsGUI();
+            base.serializedObject.ApplyModifiedProperties();
+        }
+    }
+}

Editor/NonDrawingGraphicEditor.cs.meta

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+fileFormatVersion: 2
+guid: ee2802949feca4c4c934331b6a0dc379
+timeCreated: 1483566748
+licenseType: Free
+MonoImporter:
+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

Scripts/Utilities/NonDrawingGraphic.cs

@@ -0,0 +1,21 @@
+/// Credit Slipp Douglas Thompson 
+/// Sourced from - https://gist.github.com/capnslipp/349c18283f2fea316369
+
+namespace UnityEngine.UI.Extensions
+{
+    /// A concrete subclass of the Unity UI `Graphic` class that just skips drawing.
+    /// Useful for providing a raycast target without actually drawing anything.
+    [AddComponentMenu("Layout/Extensions/NonDrawingGraphic")]
+    public class NonDrawingGraphic : MaskableGraphic
+    {
+        public override void SetMaterialDirty() { return; }
+        public override void SetVerticesDirty() { return; }
+
+        /// Probably not necessary since the chain of calls `Rebuild()`->`UpdateGeometry()`->`DoMeshGeneration()`->`OnPopulateMesh()` won't happen; so here really just as a fail-safe.
+        protected override void OnPopulateMesh(VertexHelper vh)
+        {
+            vh.Clear();
+            return;
+        }
+    }
+}

Scripts/Utilities/NonDrawingGraphic.cs.meta

@@ -0,0 +1,12 @@
+fileFormatVersion: 2
+guid: 51db53697a53f7a479b8570674dae649
+timeCreated: 1483541456
+licenseType: Free
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+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
+  assetBundleName: 
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