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()

SongObject.gd

@@ -1,4 +1,4 @@
-extends Node
+extends RefCounted
 
 class_name SongObject
 
@@ -8,7 +8,8 @@ var song_title: String
 
 var soundtrack_title: String
 
-var players_given_point: Array[int] = []
+## Ids of the players who got a point for this song.
+var players_given_point: Array[String] = []
 
 var is_answered: bool = false
 
@@ -40,16 +41,14 @@ func get_song_info() -> String:
 	else:
 		return "??? - ???"
 
-func add_point(id: int) -> void:
+func add_point(player_id: String) -> void:
 	print("add_point")
-	players_given_point.append(id)
-	players_given_point.sort()
+	if !players_given_point.has(player_id):
+		players_given_point.append(player_id)
 
-func remove_point(id: int) -> void:
+func remove_point(player_id: String) -> void:
 	print("remove_point")
-	if players_given_point.has(id):
-		players_given_point.remove_at(players_given_point.find(id))
-	players_given_point.sort()
+	players_given_point.erase(player_id)
 
 func _to_string() -> String:
 	var format_string: String = "song_number: %d | soundtrack_title: %s | song_title: %s | is_answered: %s | has_played: %s | is_playing: %s"