Add Mission::get_book_decals_visible and ::set_book_decals_visible.
DynamicLight: add new radius property. StaticLight: new object class.
Camera: new struct. Player: remove attach_camera and detach_camera methods (now in Camera). AI: rename notices_cameras to notices_watchers for clarity.
CreatureAttachmentLink: add joint_rotation. ModelsTweq: remove use_creature_scale (not applicable). Add TODO notes for RotateTweq::link_relative and ScaleTweq::affect_creature_scale.
Interface: split off from Mission; add Element enum and {get,set}_element_visible methods. Camera: should be class, not struct. Update TODO.