feature<Remote>: add 'Prune' context menu for remote to prune dead branches without fetching

src/Views/Popups/Prune.xaml

@@ -0,0 +1,10 @@
+<controls:PopupWidget 
+    x:Class="SourceGit.Views.Popups.Prune"
+    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
+    xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
+    xmlns:controls="clr-namespace:SourceGit.Views.Controls"
+    mc:Ignorable="d" 
+    d:DesignWidth="500" Height="100">
+</controls:PopupWidget>

src/Views/Popups/Prune.xaml.cs

@@ -0,0 +1,30 @@
+using System.Threading.Tasks;
+
+namespace SourceGit.Views.Popups {
+    /// <summary>
+    ///     清理远程已删除分支
+    /// </summary>
+    public partial class Prune : Controls.PopupWidget {
+        private string repo = null;
+        private string remote = null;
+
+        public Prune(string repo, string remote) {
+            this.repo = repo;
+            this.remote = remote;
+            InitializeComponent();
+        }
+
+        public override string GetTitle() {
+            return App.Text("RemoteCM.Prune");
+        }
+
+        public override Task<bool> Start() {
+            return Task.Run(() => {
+                Models.Watcher.SetEnabled(repo, false);
+                var succ = new Commands.Remote(repo).Prune(remote);
+                Models.Watcher.SetEnabled(repo, true);
+                return succ;
+            });
+        }
+    }
+}

src/Views/Widgets/Dashboard.xaml.cs

@@ -745,21 +745,28 @@ namespace SourceGit.Views.Widgets {
 
         private void FillRemoteContextMenu(ContextMenu menu, Models.Remote remote) {
             var fetch = new MenuItem();
-            fetch.Header = App.Text("RemoteCM.Fetch", remote.Name);
+            fetch.Header = App.Text("RemoteCM.Fetch");
             fetch.Click += (o, e) => {
                 new Popups.Fetch(repo, remote.Name).Show();
                 e.Handled = true;
             };
 
+            var prune = new MenuItem();
+            prune.Header = App.Text("RemoteCM.Prune");
+            prune.Click += (o, e) => {
+                new Popups.Prune(repo.Path, remote.Name).ShowAndStart();
+                e.Handled = true;
+            };
+
             var edit = new MenuItem();
-            edit.Header = App.Text("RemoteCM.Edit", remote.Name);
+            edit.Header = App.Text("RemoteCM.Edit");
             edit.Click += (o, e) => {
                 new Popups.Remote(repo, remote).Show();
                 e.Handled = true;
             };
 
             var delete = new MenuItem();
-            delete.Header = App.Text("RemoteCM.Delete", remote.Name);
+            delete.Header = App.Text("RemoteCM.Delete");
             delete.Click += (o, e) => {
                 new Popups.DeleteRemote(repo.Path, remote.Name).Show();
                 e.Handled = true;
@@ -773,6 +780,7 @@ namespace SourceGit.Views.Widgets {
             };
 
             menu.Items.Add(fetch);
+            menu.Items.Add(prune);
             menu.Items.Add(new Separator());
             menu.Items.Add(edit);
             menu.Items.Add(delete);