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.

tests/integration/test_inspiration_list.gd

@@ -15,7 +15,7 @@ func before_test() -> void:
 	Settings.inspiration_list_speed = 0
 	_server = FakeHttpTransport.new().install()
 	_server.respond_json("/music/all", SOUNDTRACKS)
-	_runner = scene_runner("res://InspirationList.tscn")
+	_runner = scene_runner("res://quiz/InspirationList.tscn")
 	_list = _runner.scene()