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.

Demos3/ImplicitCloth/stan/Cloth.h

@@ -0,0 +1,18 @@
+#ifndef STAN_CLOTH_H
+#define STAN_CLOTH_H
+
+#include "SpringNetwork.h"
+
+class Cloth : public SpringNetwork
+{
+ public:
+       int w,h;
+       
+       float3 color; // for debug rendering
+       Cloth(const char* _name,int _n);
+       ~Cloth();
+};
+
+Cloth *ClothCreate(int w,int h,float size);
+
+#endif //STAN_CLOTH_H