Follow the GDScript style guide in every script

- Types on every parameter, return value and variable, and snake_case names
  (the player name limit is the constant MAX_NAME_LENGTH).
- Spelling fixes: *_triggered, character_selected, separator, caught_errors.
  The server's catched_errors key stays as the server sends it.
- Signals are connected with signal.connect() instead of by name.
- Code is ordered signals, constants, exported vars, vars, @onready vars,
  functions, with @onready on one line and two blank lines between functions.
- Every script starts with a ## description. Template comments, old LOC notes
  and commented-out code are gone, apart from the local play code.
- Lines are at most 100 characters, apart from the local play path.
- The screenshot tour turns off the blinking text cursor so pictures match.

song_loader.gd

@@ -8,6 +8,7 @@ extends Node
 
 ## Emitted when the songs already in the server playlist have been loaded into the
 ## Playlist.
+
 signal song_list_loaded
 
 ## Emitted when a new song has been downloaded and added to the Playlist.
@@ -21,7 +22,7 @@ var retry_seconds: float = 5.0
 ## Preloading waits for the list, because loading the list clears the playlist.
 func load_song_list() -> void:
 	GameLog.debug("load_song_list")
-	var song_list_fetched: Callable = func song_list_fetched(data) -> void:
+	var song_list_fetched: Callable = func song_list_fetched(data: Variant) -> void:
 		Playlist.clear_song_list()
 		if typeof(data) == TYPE_ARRAY:
 			for d: Dictionary in data: