More modernization

- Split generic "common" libraries into specific libraries
- Use other packages in lieu of custom code
- General cleanup

Application/Options/FeedWindow.xaml.cs

@@ -1,4 +1,4 @@
-using Common.Wpf.Extensions;
+using CKaczor.Wpf.Validation;
 using System.Linq;
 using System.Windows;
 using System.Windows.Controls;