[#48] Billing: Add custom modifiers for members

Elwig/Documents/CreditNote.cs

@@ -20,6 +20,7 @@ namespace Elwig.Documents {
         public decimal MemberTotalUnderDelivery;
         public int MemberAutoBusinessShares;
         public decimal MemberAutoBusinessSharesAmount;
+        public PaymentCustom? CustomPayment;
 
         public CreditNote(
             AppDbContext ctx,
@@ -28,6 +29,7 @@ namespace Elwig.Documents {
             bool considerContractPenalties,
             bool considerTotalPenalty,
             bool considerAutoBusinessShares,
+            bool considerCustomModifiers,
             Dictionary<string, UnderDelivery>? underDeliveries = null
         ) :
             base($"{Name} {(p.Credit != null ? $"Nr. {p.Credit.Year}/{p.Credit.TgNr:000}" : p.Member.Name)} – {p.Variant.Name}", p.Member) {
@@ -85,5 +87,8 @@ namespace Elwig.Documents {
                     .Where(u => u.Item3 != 0)
                     .ToList();
             }
+            if (considerCustomModifiers) {
+                CustomPayment = ctx.CustomPayments.Find(p.Year, p.MgNr);
+            }
         }
     }}