Landing page: Display "copyright" if no license is selected

InvenioRDM allows the selection of 0 licenses for a dataset. This effectively means that the copyright applies legally and the users can't reuse the dataset without asking the content creator/uploader for permissions (e.g. via email).

We should make this clear by displaying "copyright applies" (or similar) where the selected licenses are usually displayed. Maybe we should also add a visible banner on the landing page if no license is selected.