Ground work for Wino Calendar. (#475)

Wino Calendar abstractions.

Wino.Core.UWP/Selectors/AppThemePreviewTemplateSelector.cs

@@ -0,0 +1,25 @@
+using Windows.UI.Xaml;
+using Windows.UI.Xaml.Controls;
+using Wino.Core.UWP.Models.Personalization;
+
+namespace Wino.Core.UWP.Selectors
+{
+    public class AppThemePreviewTemplateSelector : DataTemplateSelector
+    {
+        public DataTemplate SystemThemeTemplate { get; set; }
+        public DataTemplate PreDefinedThemeTemplate { get; set; }
+        public DataTemplate CustomAppTemplate { get; set; }
+
+        protected override DataTemplate SelectTemplateCore(object item)
+        {
+            if (item is SystemAppTheme)
+                return SystemThemeTemplate;
+            else if (item is PreDefinedAppTheme)
+                return PreDefinedThemeTemplate;
+            else if (item is CustomAppTheme)
+                return CustomAppTemplate;
+
+            return base.SelectTemplateCore(item);
+        }
+    }
+}