Editor: Keyboard navigation of the sidebar scene graph

Added keyboard navigation to the FancySelect control displayed in the sidebar, initially enabling the use of the up or down arrows keys to move through items. Also revised the scrolling logic as it didn't quite match normal control behavior or work correctly in all cases. This is probably best depicted with a screencast: http://screencast.com/t/NYnSeueyge. The key issues seemed to be:
* Some items fail to scroll into view - the first item requiring scroll doesn't fire correctly and selection occurs off-screen 
* An inconsistency between scroll up and scroll down behavior, where scroll down pages while scroll up single steps. More often scrollable controls tend to push one step in the required direction as needed.

Not sure if it's a feature you'd like to include but figured it was worth checking