ChartWindow: Automatically calculate variant when saved

Elwig/Windows/PaymentVariantsWindow.xaml.cs

@@ -251,10 +251,10 @@ namespace Elwig.Windows {
                     foreach (int mgnr in currentPayments.Keys) {
                         var c = currentPayments[mgnr];
                         var l = lastPayments[mgnr];
-                        vatSum += (c.Amount - l.Amount) * (c.Member.IsBuchführend ? 0.1m : 0.13m);
+                        vatSum += (c.Amount - l.Amount) * (decimal)(c.Member.IsBuchführend ? v.Season.VatNormal : v.Season.VatFlatrate);
                     }
                 } else {
-                    vatSum = currentPayments.Sum(e => e.Value.Amount * (e.Value.Member.IsBuchführend ? 0.1m : 0.13m));
+                    vatSum = currentPayments.Sum(e => e.Value.Amount * (decimal)(e.Value.Member.IsBuchführend ? v.Season.VatNormal : v.Season.VatFlatrate));
                 }
                 vatText = $"~{vatSum:N2} {sym}";
                 deductionText = $"- {sym}";