Add the ability to enable / disable and check for the editable property of a rendering engine. Implement for all three backends and extend the sample, document and unit test.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/SOC2011_WEBVIEW@68193 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/webview.h

@@ -281,13 +281,13 @@ public:
         SetPage(stream.GetString(), baseUrl);
     }
 
+    virtual void SetEditable(bool enable = true) = 0;
+    virtual bool IsEditable() = 0;
+
     // TODO:
     //     wxString GetSelection();                         // maybe?
     //     void SetSelection(...);                          // maybe?
 
-    //     void MakeEditable(bool enable = true);           // maybe?
-    //     bool IsEditable();                               // maybe?
-
     //     void EnableJavascript(bool enabled);             // maybe?
     //     wxString RunScript(const wxString& javascript);  // maybe?