Create a shared project with all Win App common files (8.1 and 10)

Finally use the dependency injected Resource Service

WinAppCommon/Converters/NullToBooleanConverter.cs

@@ -0,0 +1,18 @@
+using System;
+using Windows.UI.Xaml.Data;
+
+namespace ModernKeePass.Converters
+{
+    public class NullToBooleanConverter : IValueConverter
+    {
+        public object Convert(object value, Type targetType, object parameter, string language)
+        {
+            return value != null;
+        }
+
+        public object ConvertBack(object value, Type targetType, object parameter, string language)
+        {
+            throw new NotImplementedException();
+        }
+    }
+}