More modernization

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

Application/Options/CheckedListItem.cs

@@ -0,0 +1,41 @@
+using System.ComponentModel;
+
+namespace FeedCenter.Options;
+
+public class CheckedListItem<T> : INotifyPropertyChanged
+{
+    public event PropertyChangedEventHandler PropertyChanged;
+
+    private bool _isChecked;
+    private readonly T _item;
+
+    public CheckedListItem() { }
+
+    public CheckedListItem(T item, bool isChecked = false)
+    {
+        _item = item;
+        _isChecked = isChecked;
+    }
+
+    public T Item
+    {
+        get => _item;
+        init
+        {
+            _item = value;
+
+            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs("Item"));
+        }
+    }
+
+    public bool IsChecked
+    {
+        get => _isChecked;
+        set
+        {
+            _isChecked = value;
+
+            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs("IsChecked"));
+        }
+    }
+}