Added DateTimeToColorConverter

InABox.Avalonia/Converters/DateTimeToColorConverter.cs

@@ -0,0 +1,20 @@
+using Avalonia.Media;
+
+namespace InABox.Avalonia.Converters;
+
+public class DateTimeToColorConverter : AbstractConverter<DateTime,IBrush?>
+{
+
+    public DateTime? Threshold { get; set; } = null;    
+    
+    public IBrush? Expired{ get; set; }
+        
+    public IBrush? Current { get; set; }
+        
+    protected override IBrush? Convert(DateTime value, object? parameter = null)
+    {
+        var threshold = Threshold ?? DateTime.Now;
+        return value < threshold ? Expired : Current;
+    }
+
+}