Tidies the code a bit.
Fixes SC.View#animate to work with centerX & centerY.  You can now animate `centerX` and `centerY` adjustments.
Fixes animation bug where animating multiple keys in which some do not actually change value resulted in leftover animation styles.  Includes unit test.
Adds support for automatically animating margin-left and margin-top when centerX or centerY layouts are used and the height or width changes.  This makes centered height and width animations smooth.  Includes unit test.
Fixes bug preventing cancelling in place for CSS transform animations.  Updated unit test.