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/webview.h

@@ -164,7 +164,7 @@ class wxWebViewHistoryItem
 {
 public:
     /**
-        Construtor.
+        Constructor.
     */
     wxWebViewHistoryItem(const wxString& url, const wxString& title);