Returned by usePlaylistMemberships to AddToPlaylistModal and
DumpCreateModal, for their PlaylistMembershipPanel.
Empty while loading, and when the load failed.
loading: boolean
toggle: (membership: PlaylistMembership) => Promise<void>
Adds the dump to the playlist or takes it out on the server, and shows it only once the server agrees. A refusal or a dropped connection changes nothing.
add: (membership: PlaylistMembership) => void
Puts first a playlist the panel just created with the dump in it.