Add a new controller event for when a virtual entity is going to be replaced by a physical one

[christophe-calmejane]

If the controller has loaded a virtual entity and an entity with the same entityID is detected on the network, the virtual one should be removed to let the physical one take it's place. When being removed that way, it should be forwarded to the application layer though an observer method so it has a chance to store it, or synchronize it with the physical entity.