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*

interface/wx/treelist.h

@@ -90,7 +90,7 @@ public:
     /**
         Default constructor.
 
-        Notice that this class is not copyable, comparators are not passed by
+        Notice that this class is not copiable, comparators are not passed by
         value.
      */
     wxTreeListItemComparator();