Use wx-prefixed macros throughout the repository.

Change {DECLARE,IMPLEMENT}_*CLASS and {DECLARE,BEGIN,END}_EVENT_TABLE
occurrences to use the wx-prefixed version of the macros.

samples/help/demo.cpp

@@ -273,7 +273,7 @@ wxEND_EVENT_TABLE()
 // static object for many reasons) and also declares the accessor function
 // wxGetApp() which will return the reference of the right type (i.e. MyApp and
 // not wxApp)
-IMPLEMENT_APP(MyApp)
+wxIMPLEMENT_APP(MyApp);
 
 // ============================================================================
 // implementation