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

Elwig/ViewModels/AreaComAdminViewModel.cs

@@ -20,7 +20,11 @@ namespace Elwig.ViewModels {
         }
 
         [ObservableProperty]
-        private bool _showOnlyActiveAreaComs;
+        private string? _filterSeasonString;
+        public int? FilterSeason {
+            get => int.TryParse(FilterSeasonString, out var year) ? year : null;
+            set => FilterSeasonString = $"{value}";
+        }
 
         [ObservableProperty]
         private string? _fbNrString;
@@ -46,6 +50,8 @@ namespace Elwig.ViewModels {
             get => int.TryParse(YearToString, out var year) ? year : null;
             set => YearToString = $"{value}";
         }
+        [ObservableProperty]
+        private string? _period;
 
         [ObservableProperty]
         private AreaComType? _areaComType;