Add calendar control

Closes #101

src/Spectre.Console/IHasCulture.cs

@@ -0,0 +1,15 @@
+using System.Globalization;
+
+namespace Spectre.Console
+{
+    /// <summary>
+    /// Represents something that has a culture.
+    /// </summary>
+    public interface IHasCulture
+    {
+        /// <summary>
+        /// Gets or sets the culture.
+        /// </summary>
+        CultureInfo Culture { get; set; }
+    }
+}