Log through a GameLog autoload instead of print()

GameLog.debug() prints only in debug builds, and GameLog.warning() reports
problems such as unexpected server data or failed downloads.

project.godot

@@ -22,6 +22,7 @@ config/icon="res://icon.svg"
 
 [autoload]
 
+GameLog="*res://game_log.gd"
 Settings="*res://Settings.gd"
 Playlist="*res://playlist.gd"
 MusicServerClient="*res://music_server_client.gd"