project: reorganize the structure of the project.

* remove dotnet-tool.json because the project does not rely on any dotnet tools.
* remove Directory.Build.props because the solution has only one project.
* move src/SourceGit to src. It's not needed to put all sources into a subfolder of src since there's only one project.

src/Views/ChangeViewModeSwitcher.axaml.cs

@@ -0,0 +1,28 @@
+using Avalonia;
+using Avalonia.Controls;
+
+namespace SourceGit.Views
+{
+    public partial class ChangeViewModeSwitcher : UserControl
+    {
+        public static readonly StyledProperty<Models.ChangeViewMode> ViewModeProperty =
+            AvaloniaProperty.Register<ChangeViewModeSwitcher, Models.ChangeViewMode>(nameof(ViewMode));
+
+        public Models.ChangeViewMode ViewMode
+        {
+            get => GetValue(ViewModeProperty);
+            set => SetValue(ViewModeProperty, value);
+        }
+
+        public ChangeViewModeSwitcher()
+        {
+            DataContext = this;
+            InitializeComponent();
+        }
+
+        public void SwitchMode(object param)
+        {
+            ViewMode = (Models.ChangeViewMode)param;
+        }
+    }
+}