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/scroll_to_end_container.gd

@@ -0,0 +1,12 @@
+class_name ScrollToEndContainer
+extends ScrollContainer
+## A scroll container that scrolls to the end whenever its content grows, so the newest
+## item is always in view.
+
+var max_value: float = 0.0
+
+
+func _draw() -> void:
+	if max_value != get_v_scroll_bar().max_value:
+		max_value = get_v_scroll_bar().max_value
+		scroll_vertical = int(max_value)