Ground work for Wino Calendar. (#475)

Wino Calendar abstractions.

Wino.Core.UWP/Converters/GridLengthConverter.cs

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+using System;
+using Windows.UI.Xaml.Data;
+using Windows.UI.Xaml;
+
+namespace Wino.Converters
+{
+    public class GridLengthConverter : IValueConverter
+    {
+        public object Convert(object value, Type targetType, object parameter, string language)
+        {
+            if (value is double doubleValue)
+            {
+                return new GridLength(doubleValue);
+            }
+            return new GridLength(1, GridUnitType.Auto);
+        }
+
+        public object ConvertBack(object value, Type targetType, object parameter, string language)
+        {
+            if (value is GridLength gridLength)
+            {
+                return gridLength.Value;
+            }
+            return 0.0;
+        }
+    }
+}

Wino.Core.UWP/Converters/ReverseBooleanConverter.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using Windows.UI.Xaml.Data;
+
+namespace Wino.Converters
+{
+    public class ReverseBooleanConverter : IValueConverter
+    {
+        public object Convert(object value, Type targetType, object parameter, string language)
+        {
+            if (value is bool boolval)
+                return !boolval;
+
+            return false;
+        }
+
+        public object ConvertBack(object value, Type targetType, object parameter, string language)
+        {
+            throw new NotImplementedException();
+        }
+    }
+}

Wino.Core.UWP/Converters/ReverseBooleanToVisibilityConverter.cs

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+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();
+        }
+    }
+}