Outsource many methods from MemberAdminWindow to abstract classes

Elwig/Windows/ContextWindow.cs

@@ -0,0 +1,23 @@
+using Elwig.Helpers;
+using System;
+using System.Collections.Generic;
+using System.ComponentModel;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using System.Windows;
+
+namespace Elwig.Windows {
+    public abstract class ContextWindow : Window {
+        protected readonly AppDbContext Context;
+
+        public ContextWindow() : base() {
+            Context = new();
+        }
+
+        protected override void OnClosing(CancelEventArgs evt) {
+            Context.Dispose();
+            base.OnClosing(evt);
+        }
+    }
+}