Delete old, wrong, commented-out volumetric light/filter calculation code.
New TODO items.
Update world, rename 'make-solid-material-node' to 'make-homogeneous-node',
change default Inet server verbosity to WARNINGS, and default port
(since there are old clients still trying to help render using buggy tracing
algorithms) to 31149.
Fixed: HOME/END keys were mixed up.
Refactor render tasks.

Tracer has 'mode' property that determines how to render.
PixelRayIterators are now asked for image data size.
RenderTasks know trace mode.
Work towards overhauling UI code.