Name popups *Popup and give scripts, scenes and classes matching names

Every popup is now called *Popup instead of *Window in its file, root node,
node name, class and variable, and PopupWindow becomes BasePopup. Player is
PlayerRow, SongListObject is SongRow and Character is CharacterCard. Script
files are snake_case and scene files PascalCase, each matching its class or
root node, and LightGrayTheme.tres is light_gray_theme.tres.

song_object.gd

@@ -0,0 +1,55 @@
+extends RefCounted
+
+class_name SongObject
+
+var song_number: int
+
+var song_title: String
+
+var soundtrack_title: String
+
+## Ids of the players who got a point for this song.
+var players_given_point: Array[String] = []
+
+var is_answered: bool = false
+
+var has_played: bool = false
+
+var is_playing: bool = false
+
+var song: AudioStream
+
+func get_soundtrack_title() -> String:
+	if is_answered:
+		return soundtrack_title
+	else:
+		return "????????"
+
+func get_song_title() -> String:
+	if is_answered:
+		return song_title
+	else:
+		return "??????"
+
+func get_song_info() -> String:
+	if Settings.is_debug:
+		var format_string: String = "%d. %s - %s | played: %s | answered: %s"
+		return format_string % [(song_number + 1), soundtrack_title, song_title, has_played, is_answered]
+	elif is_answered:
+		var format_string: String = "%d. %s - %s"
+		return format_string % [(song_number + 1), soundtrack_title, song_title]
+	else:
+		return "??? - ???"
+
+func add_point(player_id: String) -> void:
+	GameLog.debug("add_point")
+	if !players_given_point.has(player_id):
+		players_given_point.append(player_id)
+
+func remove_point(player_id: String) -> void:
+	GameLog.debug("remove_point")
+	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"
+	return format_string % [(song_number), soundtrack_title, song_title, is_answered, has_played, is_playing]