Fix spelling in comments and documentation using codespell

Apply the utility from https://github.com/codespell-project/codespell/
to fix spelling issues in the headers under both include and interface
directories and add a file with a couple of exceptions.

The exact command line used was:

    $ codespell -w -I misc/scripts/codespell.ignore -i 3 in*

include/wx/dnd.h

@@ -187,9 +187,9 @@ public:
     virtual bool GetData() = 0;
 
     // sets the default action for drag and drop:
-    // use wxDragMove or wxDragCopy to set deafult action to move or copy
+    // use wxDragMove or wxDragCopy to set default action to move or copy
     // and use wxDragNone (default) to set default action specified by
-    // initialization of draging (see wxDropSourceBase::DoDragDrop())
+    // initialization of dragging (see wxDropSourceBase::DoDragDrop())
     void SetDefaultAction(wxDragResult action)
         { m_defaultAction = action; }