[#48] Billing: Add custom modifiers for members

Elwig/Helpers/AppDbContext.cs

@@ -57,6 +57,7 @@ namespace Elwig.Helpers {
         public DbSet<PaymentVar> PaymentVariants { get; private set; }
         public DbSet<PaymentMember> MemberPayments { get; private set; }
         public DbSet<PaymentDeliveryPart> PaymentDeliveryParts { get; private set; }
+        public DbSet<PaymentCustom> CustomPayments { get; private set; }
         public DbSet<Credit> Credits { get; private set; }
 
         public DbSet<OverUnderDeliveryRow> OverUnderDeliveryRows { get; private set; }