Add a btIDEbugDraw::clearLines, helps multi-threaded rendering of lines (while updating those lines in a dynamics world in a different thread)

Expose COV_ENABLE_VR_RENDER_CONTROLLERS, to enable/disable rendering of controllers (and some frames) in VR
Expose COV_ENABLE_RENDERING to enable/disable rendering.
Fix some multi-threading issues (potential crashes), related to debug drawing/rendering in one thread, while changing the dynamics world/removing/resetSimulation in a different thread.

examples/SharedMemory/PhysicsServerSharedMemory.h

@@ -42,7 +42,7 @@ public:
 	//and for physics visualization. The idea is that physicsDebugDraw can also send wireframe
 	//to a physics client, over shared memory
 	void    physicsDebugDraw(int debugDrawFlags);
-	void    renderScene();
+	void    renderScene(int renderFlags);
 
 	void enableCommandLogging(bool enable, const char* fileName);
 	void replayFromLogFile(const char* fileName);