Improve the `scrollbars` example

## What problem does this solve or what need does it fill?

The current `scrollbars` example just has a vertical scrolling list in the top left and is kind of ugly.
It should be centered and displays a horizontal scrollbar even though it doesn't scroll horizontally.

## What solution would you like?

Four cases:
1. The current vertical scrolling list but remove the horizontal scrollbar.
2. A horizontally scrolling list of icons.
3. A grid that scrolls both horizontally and vertically.
4. A vertically scrolling list of multiple horizontally scrolling lists.

Varied styling for the each set of scrollbars and thumbs.
Bonus if you could do a really fancy set using a UI material or texture slicing.

Could be one or multiple PRs.