My bad, it's because you're using a KinematicBody and I used the wrong name, there's an option in Rigidbody called Angular lock. I think though if you switch to rigidbody this method will work well if all you want to do is rotate and move around the characters Doom 1 style.
1:55 for relevant information.
Oh as for getting the camera in another scene I'm actually not sure on that one, I'm not 100% sure why you would do that in the first place, shouldn't you have two cameras in each scene? Would have thought the only one necessary for that is a player unless you're doing something special I don't know about.