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/power/power.cpp

@@ -274,4 +274,4 @@ public:
     }
 };
 
-IMPLEMENT_APP(MyApp)
+wxIMPLEMENT_APP(MyApp);