add ImplicitCloth demo, by Stan Melax

add SimpleOpenGL3App, used in ImplicitCloth demo. The Bullet 3.x demos should use this as a template, it will clean up some of the mess.

btgui/OpenGLWindow/Win32Window.cpp

@@ -17,7 +17,7 @@ subject to the following restrictions:
 #include "Win32Window.h"
 
 #include "OpenGLInclude.h"
-#include "Bullet3Common/b3Vector3.h"
+
 #include <wchar.h>
 static InternalData2* sData = 0;