Assets Nebula Spheres

This update adds nebula spheres that do not render clouds along the horizon. These nebula spheres render clouds straight above and straight below when the X rotation and Z rotation of the CUA are set to 0 degrees. A large ground asset is needed to hide the clouds down below. These nebula spheres are labelled "nebula tapered horizon type 1, 2 and 3" in the asset name of the bundle. A new demo scene 4 is included to demonstrate one of the new nebula spheres as illustrated in the last image below.

This update adds grayscale options for all 11 nebula effects as well as five new textures which include:

- aqua
- briar patch
- milky way
- mist
- organic compounds

This update adds a nebula editor that enables the scale, colors and opacity of the nebula spheres to be changed dynamically in your scene. Simply add the nebula_editor.cslist plugin to the CUA.