App: Rename FocusPaymentVariantsWindow to FocusPaymentVariants

Elwig/App.xaml.cs

@@ -241,7 +241,7 @@ namespace Elwig {
             return w;
         }
 
-        public static PaymentVariantsWindow FocusPaymentVariantsWindow(int year) {
+        public static PaymentVariantsWindow FocusPaymentVariants(int year) {
             return FocusWindow<PaymentVariantsWindow>(() => new(year), w => w.Year == year);
         }