Sort the scripts and scenes into folders

main/ holds the main window and top bar, quiz/ the quiz and its parts,
player/ the music player, popups/ every popup and what they share, data/ the
songs, players, playlist and settings, server/ the MusicServer client,
common/ the list row and GameLog, and themes/ the themes and style boxes.

quiz/music_list_panel.gd

@@ -0,0 +1,26 @@
+class_name MusicListPanel
+extends PanelContainer
+## The list of songs in the playlist, one row per song.
+
+## Emitted when the row of song number [param song_no] is clicked.
+
+signal song_clicked(song_no: int)
+
+var _song_list_object: PackedScene = preload("res://quiz/SongRow.tscn")
+
+@onready var _rows: VBoxContainer = %MusicList
+
+
+## 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 new_song_list_object: SongRow = _song_list_object.instantiate()
+		new_song_list_object.song_object = s
+		new_song_list_object.gui_input.connect(_on_row_input.bind(s.song_number))
+		_rows.add_child(new_song_list_object)
+
+
+func _on_row_input(event: InputEvent, song_no: int) -> void:
+	if event is InputEventMouseButton && event.pressed && event.button_index == MOUSE_BUTTON_LEFT:
+		song_clicked.emit(song_no)