Scene2DUI scroll bars can change sides, implement scrollbar test, format tests list

Three changes:
- vertical and horizontal scroll bars in scene2d ui can be set to left/right, or top/bottom respectively.
![2013-10-06-124525_642x509_scrot](https://f.cloud.github.com/assets/1393288/1276149/28b6db2c-2e42-11e3-9220-6d7fbb419277.png)


- implemented a test for scroll bars (ScrollPaneScrollBarsTest in above pic)
- formatted and alphabetized the list of tests in utils.GdxTests (better readability, easier to add new tests)

If anyone has a project/game with ScrollPane it would be nice if you could test changing the scroll bar locations with these two methods:
- setVScrollBarAtRight(false);
- setHScrollBarAtBottom(false);