Untie list funcionality from uui-ref

[julczka]

I'd like to propose a change to uui-ref-list and uui-ref. In my opinion, it would be useful to transform these two into more generic components - uui-list and uui-list-item and that way make them more flexible and not that tightly related to backoffice.

The list component could basically stay the same except for the tag name. The list item should also stay more-less the same except it could contain a slot, so you can compose it with some node reference, or pretty much whatever you want.

This would make the list component more generic and flexible.