Keeps the playlists on screen up to date, in lists, on a playlist's page and
on a dump's page. WSProvider emits it as a playlist event on each
playlist_* message; lists apply it through usePlaylistListSync, a
playlist's page through usePlaylist. Which fields are set depends on
type.
type: "created" | "updated" | "deleted" | "dumps_updated"
playlistId: string
optional
userId: string
The owner's id, set when deleted.
optional
dumpIds: string[]
Set when the dumps changed. It lists only the dumps this user may see, in order.
optional
lastDumpAt: Date
With dumpIds, when the latest of them was added; undefined when there
is none.