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/song_controls.gd

@@ -0,0 +1,27 @@
+class_name SongControls
+extends Control
+## The buttons for the song that is playing: show the answer, and go to the next song.
+
+signal show_answer_pressed
+signal next_pressed
+
+@onready var show_answer_button: Button = $ShowAnswerButton
+@onready var next_button: Button = $NextButton
+
+
+func _ready() -> void:
+	show_answer_button.pressed.connect(show_answer_pressed.emit)
+	next_button.pressed.connect(next_pressed.emit)
+
+
+## Enables Next while there is a downloaded song to play next.
+func set_next_enabled(enabled: bool) -> void:
+	next_button.disabled = !enabled
+
+
+## Disables both buttons, e.g. while the server syncs the song list. Unlocking enables
+## Show answer again; Next comes back when the next song has been downloaded.
+func set_locked(locked: bool) -> void:
+	show_answer_button.disabled = locked
+	if locked:
+		next_button.disabled = true