Fixed sky atmosphere flickering on Mac/Intel
Added backgroundColor to Scene
Updated CHANGES.md
Merge branch 'master' into background
Merge branch 'master' into background
Updated CHANGES.md
Merge branch 'master' into background
Merge branch 'master' into background
Removed incorrect Mac/Intel fix
Rebuild logos if the offset changes.
Fix label removal bug

1. See https://groups.google.com/forum/?fromgroups=#!topic/cesium-dev/pqS_8Z5Tb1g for the initial bug report.
2. Removing a label resulted in `label._index` being incorrect, which ultimately resulted in destroyed labels remaining in the collection and the incorrect label being removed.
3. Added unit test to deomnstrate the problem.
Update CHANGES.
Merge master to background
Merge pull request #452 from AnalyticalGraphicsInc/labelRemoveBug

Fix label removal bug
Fix conic visualizer sensors

Fix incorrectly cached directions in the cone visualizer which was causing all conic sensors to have the same geometry.

This fixes #242
Merge pull request #455 from AnalyticalGraphicsInc/coneFixes

Fix conic visualizer sensors
Merge branch 'master' into background

Conflicts:
	CHANGES.md
Merge pull request #420 from AnalyticalGraphicsInc/background

Fixed sky atmosphere flickering on Mac
Merge remote-tracking branch 'origin/logoOffset' into playback
Merge remote-tracking branch 'origin/master' into playback