Ground work for Wino Calendar. (#475)

Wino Calendar abstractions.

Wino.Core.UWP/Converters/ReverseBooleanToVisibilityConverter.cs

@@ -0,0 +1,23 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using Windows.UI.Xaml;
+using Windows.UI.Xaml.Data;
+
+namespace Wino.Converters
+{
+    public class ReverseBooleanToVisibilityConverter : IValueConverter
+    {
+        public object Convert(object value, Type targetType, object parameter, string language)
+        {
+            return ((bool)value) ? Visibility.Collapsed : Visibility.Visible;
+        }
+
+        public object ConvertBack(object value, Type targetType, object parameter, string language)
+        {
+            throw new NotImplementedException();
+        }
+    }
+}