Do not display empty table's headers

What happens?

If you go to a page with a table, the header of the table is always displayed, even if the content is empty. Here is a (non-exhaustive) list of the concerned pages:

• library track's list when no tracks
• playlist modal with no playlist
• playlist detail page when no tracks in the playlist
• radio detail page
• users list (admin) (not sure if this is relevant :))
• moderation: domain's list
• favorite's list

What is expected?

We should not display an empty header, instead a paragraph like "There is no content to display" or something like that, to be adapted to the different scenarios...

If relevant, the search formular should also not be displayed.

Funkwhale version(s) affected: dev