Update resizer to handle the case where a stickyElement changes height

This change fixes a bug where resizing a window changes the height of a sticky element.  
![Screen Shot 2013-04-26 at 10 56 23 ](https://f.cloud.github.com/assets/320207/431654/c13c3722-ae8e-11e2-96a2-7146d4f00816.png)

If you've got a buttonset like the one above, and you resize the window, you can end up with something like this: 
![Screen Shot 2013-04-26 at 10 56 47 ](https://f.cloud.github.com/assets/320207/431657/d3c8f4ac-ae8e-11e2-8dc6-a65e64e5b343.png)

The answer is to recalculate the height of each stickyElement whenever a resize event happens.  This particular pull request is a bit more complicated than my first attempt, because it seems like changing the style when not necessary might introduce a performance hit by triggering a reflow.  (This is why I'm caching the height of the element in a data() of the stickyWrapper.)