Add custom renderer column to the list model example in dataview sample.

Add a column using custom renderer to the example using a list model with
attributes to test attributes support -- currently they are ignored, but this
will be fixed soon.

Also make the custom renderer display somewhat more clear as previously it
didn't depend at all on its value.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@62588 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

samples/dataview/mymodels.h

@@ -193,6 +193,7 @@ public:
         Col_EditableText,
         Col_IconText,
         Col_TextWithAttr,
+        Col_Custom,
         Col_Max
     };