Update moon imagery in sky view so phases change

[patudom]

This is important for a Cosmic Data Stories Mini on the upcoming eclipses.

In the WWT desktop client sky view, the moon image set changes as the phases change. This should be implemented in the web engine. (The moon shown in sky view shouldn't look like a full moon when it's a new moon.)

Edited to note that in particular, it looks like there is a dark shading that appears overlaid on the moon, and the amount/shape of the shading changes with the moon's phases.

Desktop client:

Web client:

[pkgw]

My guess is that the Windows client has a custom shader that implements this effect, and we'd need to port it over. But I think that the surrounding scaffolding to calculate the relevant physical parameters should basically be present in the web engine codebase already, since we have a bunch of the astronomy library code that does this kind of stuff.