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()

character.gd

@@ -35,7 +35,7 @@ func set_character_name(character_name: String) -> void:
 		character_image.expand_mode = TextureRect.EXPAND_FIT_WIDTH_PROPORTIONAL
 		character_image.stretch_mode = TextureRect.STRETCH_KEEP_ASPECT_CENTERED
 		character_image.texture = new_image
-	Settings.make_request2("/character?name=" + character_name.uri_encode(), image_fetched, true)
+	MusicServerClient.fetch_character_image(character_name, image_fetched)
 
 func _input(event: InputEvent) -> void:
 	if self.visible == true && Settings.character_select_open == true: