Add lighting to the earth.
Add option to enable/disable globe lighting.
Make sharper transition from day to night.
Fade out lighting effect on zoom in.
Make lighting fade in and out distances configurable.
Update CHANGES.md.
Merge branch 'master' into globeLighting

Conflicts:
	CHANGES.md
Make the fading distances a vec2 uniform.
Made lighting fade slightly slower.
Merge branch 'master' into globeLighting
Merge branch 'master' into globeLighting

Conflicts:
	CHANGES.md
Add CentralBody enableLighting test.
Merge branch 'master' into globeLighting

Conflicts:
	CHANGES.md
Merge remote-tracking branch 'origin/master' into globeLighting
Merge pull request #1251 from AnalyticalGraphicsInc/globeLighting

Globe Lighting