Lay out the song list's pictures and text to fit any number of players

The players' pictures sit on the right in even lines of at most four, each
ending at the row's right edge, so five pictures are 3 + 2 and seven 4 + 3.
The text takes the room they leave and wraps only when it does not fit, and
the row is as tall as the taller of the two, instead of a width fixed by
the number of pictures.

Rows are rounded and alternate like the other lists, are highlighted under
the mouse, and the playing song has an orange edge. Clicking a picture
clicks its song.

quiz/music_list_panel.gd

@@ -14,9 +14,12 @@ var _song_list_object: PackedScene = preload("res://quiz/SongRow.tscn")
 ## Shows the songs in the playlist again, so it shows their latest state.
 func refresh() -> void:
 	Settings.delete_children(_rows)
-	for s: SongObject in Playlist.get_playlist():
+	var songs: Array[SongObject] = Playlist.get_playlist()
+	for i: int in songs.size():
+		var s: SongObject = songs[i]
 		var new_song_list_object: SongRow = _song_list_object.instantiate()
 		new_song_list_object.song_object = s
+		new_song_list_object.index = i
 		new_song_list_object.gui_input.connect(_on_row_input.bind(s.song_number))
 		_rows.add_child(new_song_list_object)