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/msw/webview_ie.h

@@ -93,6 +93,10 @@ public:
     virtual void Undo();
     virtual void Redo();
 
+    //Editing functions
+    virtual void SetEditable(bool enable = true);
+    virtual bool IsEditable();
+
     // ---- IE-specific methods
 
     // FIXME: I seem to be able to access remote webpages even in offline mode...