Add time zones settings panel

DataErrorDictionary.cs

@@ -0,0 +1,42 @@
+using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.ComponentModel;
+
+namespace WorldClockStatusWindow;
+
+internal class DataErrorDictionary : Dictionary<string, List<string>>
+{
+    public event EventHandler<DataErrorsChangedEventArgs> ErrorsChanged;
+
+    private void OnErrorsChanged(string propertyName)
+    {
+        ErrorsChanged?.Invoke(this, new DataErrorsChangedEventArgs(propertyName));
+    }
+
+    public IEnumerable GetErrors(string propertyName)
+    {
+        return TryGetValue(propertyName, out var value) ? value : null;
+    }
+
+    public void AddError(string propertyName, string error)
+    {
+        if (!ContainsKey(propertyName))
+            this[propertyName] = [];
+
+        if (this[propertyName].Contains(error))
+            return;
+
+        this[propertyName].Add(error);
+        OnErrorsChanged(propertyName);
+    }
+
+    public void ClearErrors(string propertyName)
+    {
+        if (!ContainsKey(propertyName))
+            return;
+
+        Remove(propertyName);
+        OnErrorsChanged(propertyName);
+    }
+}