Initial commit

Half-baked state. Most of the UI is mostly done, but the integration
with Grist (or any other data provider) is still missing.

finish_popup.gd

@@ -0,0 +1,11 @@
+extends PopupPanel
+
+func _ready():
+	# TODO: Kontostand vorher/nachher anzeigen
+	%Label.text = """\
+	Stimmt alles?
+	
+	%s Produkte
+	%.2f€ Gesamtpreis
+	""" % [Global.cart.size(), Global.cart_total_cents]
+