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/dll/wx_exe.cpp

@@ -140,4 +140,4 @@ int MainApp::OnExit()
 }
 
 
-IMPLEMENT_APP(MainApp)
+wxIMPLEMENT_APP(MainApp);