feature<SubTree>: supports git subtree feature

src/Views/Popups/AddSubTree.xaml.cs

@@ -0,0 +1,57 @@
+using System.Threading.Tasks;
+using System.Windows.Controls;
+
+namespace SourceGit.Views.Popups {
+
+    /// <summary>
+    ///     添加子树面板
+    /// </summary>
+    public partial class AddSubTree : Controls.PopupWidget {
+        private Models.Repository repo = null;
+
+        public string Source { get; set; }
+        public string Ref { get; set; }
+        public string Prefix { get; set; }
+
+        public AddSubTree(Models.Repository repo) {
+            this.repo = repo;
+            InitializeComponent();
+        }
+
+        public override string GetTitle() {
+            return App.Text("AddSubTree");
+        }
+
+        public override Task<bool> Start() {
+            txtSource.GetBindingExpression(TextBox.TextProperty).UpdateSource();
+            if (Validation.GetHasError(txtSource)) return null;
+
+            txtPrefix.GetBindingExpression(TextBox.TextProperty).UpdateSource();
+            if (Validation.GetHasError(txtPrefix)) return null;
+
+            txtRef.GetBindingExpression(TextBox.TextProperty).UpdateSource();
+            if (Validation.GetHasError(txtRef)) return null;
+
+            var squash = chkSquash.IsChecked == true;
+            if (repo.SubTrees.FindIndex(x => x.Prefix == Prefix) >= 0) {
+                Models.Exception.Raise($"Subtree add failed. Prefix({Prefix}) already exists!");
+                return null;
+            }
+
+            return Task.Run(() => {
+                Models.Watcher.SetEnabled(repo.Path, false);
+                var succ = new Commands.SubTree(repo.Path).Add(Prefix, Source, Ref, squash, UpdateProgress);
+                if (succ) {
+                    repo.SubTrees.Add(new Models.SubTree() {
+                        Prefix = Prefix,
+                        Remote = Source,
+                    });
+                    Models.Preference.Save();
+                    Models.Watcher.Get(repo.Path)?.RefreshSubTrees();
+                }
+                Models.Watcher.SetEnabled(repo.Path, true);
+                return succ;
+            });
+        }
+    }
+}