Add saturation adjustment to imagery layers.
Add hue adjustments to imagery layers.
Update CHANGES.md.
Merge branch 'master' into hue-saturation

Conflicts:
	CHANGES.md
Tweaked CHANGES.md
Merge branch 'master' into hue-saturation

Conflicts:
	CHANGES.md
Merge branch 'master' into hue-saturation

Conflicts:
	CHANGES.md
Only add image processing code to the central body shader if the imagery layer properties change.
Merge pull request #456 from AnalyticalGraphicsInc/hue-saturation

Hue and Saturation