Seamlessly travels to the given URL by first loading the entry level in the background, switching to it, and then loading the specified level. Does not disrupt network communication or disconnect clients. You may need to implement GameModeBase::GetSeamlessTravelActorList(), PlayerController::GetSeamlessTravelActorList(), GameModeBase::PostSeamlessTravel(), and/or GameModeBase::HandleSeamlessTravelPlayer() to handle preserving any information that should be maintained (player teams, etc) This codepath is designed for worlds that use little or no level streaming and GameModes where the game state is reset/reloaded when transitioning. (like UT)