feature<Cleanup>: add toolbar button to run git gc and git lfs prune

src/Views/Popups/Cleanup.xaml

@@ -0,0 +1,12 @@
+<controls:PopupWidget x:Class="SourceGit.Views.Popups.Cleanup"
+             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="800" Height="100">
+    <Grid>
+            
+    </Grid>
+</controls:PopupWidget>

src/Views/Popups/Cleanup.xaml.cs

@@ -0,0 +1,34 @@
+using System.Threading.Tasks;
+
+namespace SourceGit.Views.Popups {
+    /// <summary>
+    ///     清理仓库
+    /// </summary>
+    public partial class Cleanup : Controls.PopupWidget {
+        private string repo;
+
+        public Cleanup(string repo) {
+            this.repo = repo;
+            InitializeComponent();
+        }
+
+        public override string GetTitle() {
+            return App.Text("Dashboard.Clean");
+        }
+
+        public override Task<bool> Start() {
+            UpdateProgress(GetTitle());
+
+            return Task.Run(() => {
+                Models.Watcher.SetEnabled(repo, false);
+                new Commands.GC(repo, UpdateProgress).Exec();
+
+                var lfs = new Commands.LFS(repo);
+                if (lfs.IsEnabled()) lfs.Prune(UpdateProgress);
+
+                Models.Watcher.SetEnabled(repo, true);
+                return true;
+            });
+        }
+    }
+}