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/ribbon/toolbar.h

@@ -315,7 +315,7 @@ public:
     virtual size_t GetToolCount() const;
 
     /**
-        Return the id assciated to the tool opaque structure.
+        Return the id associated to the tool opaque structure.
 
         The structure pointer must not be @NULL.