Improved TreeListView copy/paste support.

- Fix sorting to respect visual ordering by ID, including parent.
- Provide Ctrl-A to 'Select All'. Note that there is an extant
bug with the redraw where renderdocui will not repaint when
it gets focus back.

renderdocui/Windows/Dialogs/ConstantBufferPreviewer.cs

@@ -364,6 +364,10 @@ namespace renderdocui.Controls
                     }
                 }
             }
+            else if(e.KeyCode == Keys.A && e.Control)
+            {
+                variables.SelectAll();
+            }
         }
 
 		private BufferFormatSpecifier m_FormatSpecifier = null;