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/Init.cs

@@ -0,0 +1,51 @@
+using System.IO;
+using System.Threading.Tasks;
+
+namespace SourceGit.ViewModels
+{
+    public class Init : Popup
+    {
+        public string TargetPath
+        {
+            get => _targetPath;
+            set => SetProperty(ref _targetPath, value);
+        }
+
+        public Init(string path)
+        {
+            TargetPath = path;
+            View = new Views.Init() { DataContext = this };
+        }
+
+        public override Task<bool> Sure()
+        {
+            ProgressDescription = $"Initialize git repository at: '{_targetPath}'";
+
+            return Task.Run(() =>
+            {
+                var succ = new Commands.Init(HostPageId, _targetPath).Exec();
+                if (!succ)
+                    return false;
+
+                var gitDir = Path.GetFullPath(Path.Combine(_targetPath, ".git"));
+
+                CallUIThread(() =>
+                {
+                    var repo = Preference.AddRepository(_targetPath, gitDir);
+                    var node = new RepositoryNode()
+                    {
+                        Id = repo.FullPath,
+                        Name = Path.GetFileName(repo.FullPath),
+                        Bookmark = 0,
+                        IsRepository = true,
+                    };
+                    Preference.AddNode(node);
+                });
+
+                return true;
+            });
+        }
+
+        private string _targetPath;
+    }
+}