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/scroll/scroll.cpp

@@ -978,7 +978,7 @@ void MyFrame::OnAbout( wxCommandEvent &WXUNUSED(event) )
 // MyApp
 // ----------------------------------------------------------------------------
 
-IMPLEMENT_APP(MyApp)
+wxIMPLEMENT_APP(MyApp);
 
 bool MyApp::OnInit()
 {