Add setUserIndex/getUserIndex (int index) to btCollisionShape

Share physics setup of BasicDemo between different graphics frameworks, see Demos\BasicDemo\BasicDemoPhysicsSetup.*
Plan is to do this for all Bullet demos.
Improve gwen performance and cursor navigation for tree control.
tweak shadowmap size
SimpleOpenGL3App::registerCubeShape accepts half extents

Demos3/AllBullet2Demos/main.cpp

@@ -217,7 +217,7 @@ int main(int argc, char* argv[])
 		app->swapBuffer();
 	} while (!app->m_window->requestedExit());
 
-	selectDemo(0);
+//	selectDemo(0);
 	delete gui;
 	delete app;
 	return 0;