Move server calls to MusicServerClient and give players stable ids

Server requests move out of Settings into a new MusicServerClient
autoload with one function per endpoint. It sends requests through a
swappable HttpTransport so tests can fake the server, and it frees its
HTTPRequest nodes after use.

Players now have a UUID that never changes. Their position in
Settings.player_array is only used for the Alt+<number> keybinds.
Previously the position doubled as the id, so removing a player made
points and wins land on the wrong player, and could delete another
player's point from a song.

Also fixes:
- format_time showed 59.6 seconds as "00:60"
- searches containing regex characters such as "Q*bert" broke search
- SongObject and PlayerObject were Nodes that were never freed; they
  are now RefCounted
- search matching is split out of the UI code into find_matches()

song_list_object.gd

@@ -39,12 +39,12 @@ func set_label() -> void:
 func update_players() -> void:
 	Settings.delete_children(song_list_players)
 	if song_object != null:
-		for player_id: int in song_object.players_given_point:
-			for player: PlayerObject in Settings.player_array:
-				if player.id == player_id:
-					var texture: TextureRect = TextureRect.new()
-					texture.texture = player.character
-					texture.expand_mode = TextureRect.EXPAND_FIT_WIDTH_PROPORTIONAL
-					texture.stretch_mode = TextureRect.STRETCH_KEEP_ASPECT_CENTERED
-					texture.custom_minimum_size = Vector2(50, 25)
-					song_list_players.add_child(texture)
+		# Show players in the same order as the player list
+		for player: PlayerObject in Settings.player_array:
+			if song_object.players_given_point.has(player.id):
+				var texture: TextureRect = TextureRect.new()
+				texture.texture = player.character
+				texture.expand_mode = TextureRect.EXPAND_FIT_WIDTH_PROPORTIONAL
+				texture.stretch_mode = TextureRect.STRETCH_KEEP_ASPECT_CENTERED
+				texture.custom_minimum_size = Vector2(50, 25)
+				song_list_players.add_child(texture)