Camera cleanup

* Remove need for camera to be linked to a body. Now it just has a position (ie frame+pos within frame) and orientation.
* Restructure WorldView cameras into "controllers". No longer inherit from Camera. Instead they provide various ways of manipulating a position against a body (ship) and turning it into position + orientation for the camera.
* Since the camera no longer knows about bodies, it can't have a flag anymore to say "don't draw the body". Since every body `Render` method takes the camera anyway, we just check if the camera is inside the body and don't draw ships or cargo bodies if it is. Still need to draw space stations, cities, etc since the camera is often inside them.