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/SimpleOpenGL3App.h

@@ -0,0 +1,25 @@
+#ifndef SIMPLE_OPENGL3_APP_H
+#define SIMPLE_OPENGL3_APP_H
+
+#include "OpenGLWindow/GLInstancingRenderer.h"
+#include "OpenGLWindow/GLPrimitiveRenderer.h"
+#include "OpenGLWindow/b3gWindowInterface.h"
+
+struct SimpleOpenGL3App
+{
+	struct SimpleInternalData* m_data;
+
+	class b3gWindowInterface*	m_window;
+	class GLPrimitiveRenderer*	m_primRenderer;
+	class GLInstancingRenderer* m_instancingRenderer;
+
+	SimpleOpenGL3App(const char* title, int width,int height);
+	virtual ~SimpleOpenGL3App();
+	
+	void drawGrid(int gridSize=10);
+	void swapBuffer();
+	void drawText( const char* txt, int posX, int posY);
+
+};
+
+#endif //SIMPLE_OPENGL3_APP_H