Notify plugins on certain events (e.g. body added).

This also adds a periodic tick function to plugins, giving them periodically control over the simulation thread, even when the simulation is paused.

examples/SharedMemory/PhysicsServerSharedMemory.h

@@ -32,6 +32,8 @@ public:
 	virtual void enableRealTimeSimulation(bool enableRealTimeSim);
 	virtual bool isRealTimeSimulationEnabled() const;
 
+	virtual void tickPlugins();
+
 	//bool	supportsJointMotor(class btMultiBody* body, int linkIndex);