[#77] Entities: Add AreaComContract to group area commitments together

Elwig/Helpers/Validator.cs

@@ -580,7 +580,7 @@ namespace Elwig.Helpers {
             }
         }
 
-        public static ValidationResult CheckFbNr(TextBox input, bool required, AreaCom? c) {
+        public static ValidationResult CheckFbNr(TextBox input, bool required, AreaComContract? c) {
             var res = CheckInteger(input, required);
             if (!res.IsValid) {
                 return res;