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.

popups/AboutPopup.tscn

@@ -0,0 +1,61 @@
+[gd_scene format=3 uid="uid://cp54idaudb8dp"]
+
+[ext_resource type="Script" uid="uid://b7bh0of7olbcb" path="res://popups/about_popup.gd" id="1_about_script"]
+[ext_resource type="Theme" path="res://themes/popup_theme.tres" id="popup_theme"]
+
+[node name="AboutPopup" type="Control" unique_id=1626010355 node_paths=PackedStringArray("panel")]
+theme = ExtResource("popup_theme")
+layout_mode = 3
+anchors_preset = 15
+anchor_right = 1.0
+anchor_bottom = 1.0
+grow_horizontal = 2
+grow_vertical = 2
+script = ExtResource("1_about_script")
+panel = NodePath("AboutPanel")
+
+[node name="AboutPanel" type="Panel" parent="." unique_id=1907299275]
+unique_name_in_owner = true
+layout_mode = 0
+offset_right = 600.0
+offset_bottom = 640.0
+
+[node name="TitleLabel" type="Label" parent="AboutPanel" unique_id=200295721]
+layout_mode = 0
+offset_right = 600.0
+offset_bottom = 50.0
+text = "About"
+horizontal_alignment = 1
+vertical_alignment = 1
+
+[node name="ScrollContainer" type="ScrollContainer" parent="AboutPanel" unique_id=417677913]
+layout_mode = 0
+offset_left = 20.0
+offset_top = 50.0
+offset_right = 580.0
+offset_bottom = 630.0
+horizontal_scroll_mode = 0
+
+[node name="ContentVBox" type="VBoxContainer" parent="AboutPanel/ScrollContainer" unique_id=1746337912]
+layout_mode = 2
+size_flags_horizontal = 3
+size_flags_vertical = 3
+
+[node name="VersionLabel" type="Label" parent="AboutPanel/ScrollContainer/ContentVBox" unique_id=352884126]
+unique_name_in_owner = true
+layout_mode = 2
+size_flags_horizontal = 3
+horizontal_alignment = 1
+
+[node name="DescriptionLabel" type="Label" parent="AboutPanel/ScrollContainer/ContentVBox" unique_id=543094263]
+layout_mode = 2
+size_flags_horizontal = 3
+text = "Try your video game music knowledge with this VGM randomizer, invite your friends and see who is the best."
+horizontal_alignment = 1
+autowrap_mode = 2
+
+[node name="WhatsNewLabel" type="Label" parent="AboutPanel/ScrollContainer/ContentVBox" unique_id=1363040291]
+unique_name_in_owner = true
+layout_mode = 2
+size_flags_horizontal = 3
+autowrap_mode = 2