Clean up folder structure a bit, move .NET 3rdparty under renderdocui/

renderdocui/3rdparty/WinFormsUI/Docking/DockWindow.SplitterControl.cs

@@ -0,0 +1,28 @@
+using System;
+using System.Collections;
+using System.ComponentModel;
+using System.Drawing;
+using System.Windows.Forms;
+
+namespace WeifenLuo.WinFormsUI.Docking
+{
+    public partial class DockWindow
+    {
+        private class SplitterControl : SplitterBase
+        {
+            protected override int SplitterSize
+            {
+                get { return Measures.SplitterSize; }
+            }
+
+            protected override void StartDrag()
+            {
+                DockWindow window = Parent as DockWindow;
+                if (window == null)
+                    return;
+
+                window.DockPanel.BeginDrag(window, window.RectangleToScreen(Bounds));
+            }
+        }
+    }
+}