#41 local illumination sources

[Selden Ball]

When constructing buildings, e.g. observatories, one needs to be able to provide interior illumination sources with controllable intensity, including off.

This requires several enhancements, most of which have been discussed as future possibilities.

Suggestions, roughly in order of importance:

1. implement controllable star intensity.
It seems reasonable to me to specify the maximum value as the xxxMag value
and use that value to determine the location in the octree. Don't reorganize the octree when luminosity changes: only a small fraction of stars will be variable.

2. position and orient stars (or other illumination sources) relative to SSC reference frames. STC reference frames would be OK, but would require duplicating SSC frames in STC catalogs in order to position the illumination sources.

3. display illumination effects for ~100 simultaneous light sources. e.g. Palomar has several dozen inside lights, including those built into its control desk.

4. shadows/eclipse effects for 3D models
e.g. lights inside buildings shouldn't be seen outside
except through holes in the model, and lights in fixtures should only illuminate through the openings in the fixtures.

5. reflected illumination colored by adjacent model surfaces, preferably twice.

6. transmitted illumination colored (filtered) by translucent materials