feature<Launcher>: close tabs by context menu; collect garbage after repository closed

src/App.xaml.cs

@@ -90,6 +90,14 @@ namespace SourceGit {
             Current.MainWindow.Show();
         }
 
+        /// <summary>
+        ///     Open repository.
+        /// </summary>
+        /// <param name="repo"></param>
+        public static void Open(Git.Repository repo) {
+            (Current.MainWindow as UI.Launcher).Open(repo);
+        }
+
         /// <summary>
         ///     Deactivated event.
         /// </summary>