feat(atmosphere): Hillarie Phisically Based Atmosphere Shader

[mate-h]

Summary

This is a follow up pull request to:

https://github.com/Orillusion/orillusion/pull/376

I have separated out the atmosphere code as a separate package. It is open for feedback, some of the parameters like sun radius, displaySun are not working yet, but I will add those features back in subsequent commits as well as expose and improve the cloud coverage settings.

Demo screenshot