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/GpuDemos/main_opengl3core.cpp

@@ -84,12 +84,13 @@ enum
 };
 
 b3AlignedObjectArray<const char*> demoNames;
-int selectedDemo = 0;
+int selectedDemo = 1;
 GpuDemo::CreateFunc* allDemos[]=
 {
 		//ConcaveCompound2Scene::MyCreateFunc,
 	
 	
+	
 
 	//ConcaveSphereScene::MyCreateFunc,
 	
@@ -100,6 +101,7 @@ GpuDemo::CreateFunc* allDemos[]=
 	
 	ConcaveScene::MyCreateFunc,
 
+	
 	GpuBoxPlaneScene::MyCreateFunc,
 	GpuConstraintsDemo::MyCreateFunc,
 	//GpuConvexPlaneScene::MyCreateFunc,