Introduced new GUIEventAdatper singleton for sharing the current state between

multiple GraphicsWindows, this singleton is accessable via GUIEventEvent::getAccumulatedEventState().

Added use of this new singleton in GraphicsWindow* implementations.

Added WindowSizeHandler to osgkeyboard to help with debugging of event state
between windows.

src/osgViewer/GraphicsWindowWin32.cpp

@@ -1010,6 +1010,8 @@ void GraphicsWindowWin32::init()
 {
     if (_initialized) return;
 
+    getEventQueue()->setCurrentEventState(osgGA::GUIEventAdapter::getAccumulatedEventState().get());
+
     WindowData *windowData = _traits.get() ? dynamic_cast<WindowData*>(_traits->inheritedWindowData.get()) : 0;
     HWND windowHandle = windowData ? windowData->_hwnd : 0;