Add currency database, cleanup legacy system

big_number_progress_bar.gd

@@ -1,6 +1,6 @@
 extends HBoxContainer
 
-@export var currency: Resource = GameState.GOLD_CURRENCY
+@export var currency: Resource
 
 @onready var _label_start = $LabelStart
 @onready var _label_end = $LabelEnd
@@ -23,7 +23,10 @@ func set_limits(start: BigNumber, end: BigNumber) -> void:
 
 func _ready() -> void:
 	if currency == null:
-		currency = GameState.GOLD_CURRENCY
+		currency = CurrencyDatabase.get_currency_resource(GameState.GOLD_CURRENCY_ID)
+	if currency == null:
+		push_warning("BigNumberProgressBar '%s' has no currency configured." % String(name))
+		return
 	_currency_id = GameState.get_currency_id(currency)
 
 	GameState.currency_changed.connect(_on_currency_changed)