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. (see test for demonstration)
- implemented a test for scroll bars
- 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(true);