Property animation timeline with keyframe tweening and easing

Related to #82

As a data storyteller
I would like the camera to move around smoothly and automatically over time
So I can focus on the narrative I am trying to convey

# Feature
Add a 'camera automation timeline' interface to enable sequenced camera movements. The movements might be encoded in keyframes that contain the camera location and rotation (abstracted from the internal viewport data representation). Camera position would be animated by 'tweening' the values between keyframes. Non-linear tweens, or easings, would give a natural feeling to camera motion.

Start by reviewing related issue #82 and the existing camera and viewport concepts referenced in this issue. Define the timeline, keyframe representation, camera location and rotation abstraction, tweening, and easing behavior before implementation; done means sequenced camera movements can be automated smoothly over time.

Written by the indexing model from the issue text.