Rename ListElement props leftElements and rightElements

[michael-braun]

I think it would increase the usability of the ListItem component, when the props leftElements and rightElements are renamed to left and right. The naming would be less exact, but the typings should be enough.

So far I have not seen a leftElements-prop when developing with react. But left and right seems to be used sometimes for component composition (e.g. in the react-documentation about Composition).