feature<WorkingCopyChanges>: add the shortcut SPACE to stage/unstage the selected file

src/Views/Widgets/WorkingCopyChanges.xaml

@@ -28,14 +28,17 @@
             Visibility="Visible">
             <TreeView.Resources>
                 <RoutedUICommand x:Key="SelectWholeTreeCommand" Text="SelectWholeTree"/>
+                <RoutedUICommand x:Key="StageChangeCommand" Text="StageChange"/>
             </TreeView.Resources>
 
             <TreeView.InputBindings>
                 <KeyBinding Key="A" Modifiers="Ctrl" Command="{StaticResource SelectWholeTreeCommand}"/>
+                <KeyBinding Key="Space" Command="{StaticResource StageChangeCommand}"/>
             </TreeView.InputBindings>
 
             <TreeView.CommandBindings>
                 <CommandBinding Command="{StaticResource SelectWholeTreeCommand}" Executed="SelectWholeTree"/>
+                <CommandBinding Command="{StaticResource StageChangeCommand}" Executed="StageChange"/>
             </TreeView.CommandBindings>
             
             <controls:Tree.ItemContainerStyle>

src/Views/Widgets/WorkingCopyChanges.xaml.cs

@@ -689,6 +689,14 @@ namespace SourceGit.Views.Widgets {
         private void SelectWholeTree(object sender, ExecutedRoutedEventArgs e) {
             modeTree.SelectAll();
         }
+        
+        private void StageChange(object sender, ExecutedRoutedEventArgs e) {
+            if (!IsUnstaged) {
+                UnstageSelected();
+            } else {
+                StageSelected();
+            }
+        }
 
         private void OnTreeSelectionChanged(object sender, RoutedEventArgs e) {
             if (Mode != Models.Change.DisplayMode.Tree) return;