Need a polished demo.

[vmpstr]

It would be nice to have a polished demo for virtual-scroller element, which may include some common interaction (scrolling, item resizing, changing the theme).

This would allow us to showcase the prototype in a more or less "real" scenarios.

[domenic]

I think this is more or less done, but let's close this and reopen in fergald/virtual-scroller-demos as necessary.