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/ViewModels/LauncherPage.cs

@@ -0,0 +1,67 @@
+using System;
+
+using Avalonia.Collections;
+
+namespace SourceGit.ViewModels
+{
+    public class LauncherPage : PopupHost
+    {
+        public RepositoryNode Node
+        {
+            get => _node;
+            set => SetProperty(ref _node, value);
+        }
+
+        public object Data
+        {
+            get => _data;
+            set => SetProperty(ref _data, value);
+        }
+
+        public AvaloniaList<Models.Notification> Notifications
+        {
+            get;
+            set;
+        } = new AvaloniaList<Models.Notification>();
+
+        public LauncherPage()
+        {
+            _node = new RepositoryNode()
+            {
+                Id = Guid.NewGuid().ToString(),
+                Name = "WelcomePage",
+                Bookmark = 0,
+                IsRepository = false,
+            };
+            _data = new Welcome();
+        }
+
+        public LauncherPage(RepositoryNode node, Repository repo)
+        {
+            _node = node;
+            _data = repo;
+        }
+
+        public override string GetId()
+        {
+            return _node.Id;
+        }
+
+        public void CopyPath()
+        {
+            if (_node.IsRepository)
+                App.CopyText(_node.Id);
+        }
+
+        public void DismissNotification(object param)
+        {
+            if (param is Models.Notification notice)
+            {
+                Notifications.Remove(notice);
+            }
+        }
+
+        private RepositoryNode _node = null;
+        private object _data = null;
+    }
+}