Billing: Add functionality to collapse curves

Elwig/Models/Entities/WineAttr.cs

@@ -23,6 +23,13 @@ namespace Elwig.Models.Entities {
         [Column("fill_lower")]
         public int FillLower { get; set; }
 
+        public WineAttr() { }
+
+        public WineAttr(string attrId, string name) {
+            AttrId = attrId;
+            Name = name;
+        }
+
         public override string ToString() {
             return Name;
         }