Changed SCSelectionView to use the inverse of the brightnessComponent of the current theme's background color

Midnight has been my theme of choice for a very long time, but I was having trouble seeing the black selectionView against a black background. 

Screenshot: 
![image](https://f.cloud.github.com/assets/190671/438099/0105bce8-b0ba-11e2-829b-1e11e05f0ed7.png)


Bonus SCInvertedSelectionView, which is mostly useless, until I invert everything else.