OBJ_LOADER_DEMO: Remove most of the comments.

Instead, refer the user to example_scene.json and scene.schema.json
DOCUMENTATION: Allow scenes to support light animation
OBJ_LOADER_DEMO: Animate the point lights and spot lights.

Leave the directional light stationary
DOCUMENTATION: Velocities require bounds
OBJ_LOADER_DEMO: Re-enable light animation

This implementation is a bit gross, but it's a placeholder until a proper
Entity System can be implemented
OBJ_LOADER_DEMO: Update the light velocity values to be sane

The units are [units/ms]
COMMON: We can't assume the value of acos