Sky Cloud component editor performance improvements

[yuriy0]

Issue #, if available:

Description of changes: The Sky Cloud cloud editor component has some pathological performance characteristics which make working with it very difficult.

This merge request helps to alleviate this by calling less frequently operations which have significant performance cost (particularly in the case of volumetric clouds). (6e870b1, 6e870b1)

It also fixes a bug in which particle data is duplicated each time the editor Sky Cloud component is deactivate and reactivated (dd21292).

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.