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/Archive.cs

@@ -0,0 +1,73 @@
+using System.ComponentModel.DataAnnotations;
+using System.IO;
+using System.Threading.Tasks;
+
+namespace SourceGit.ViewModels
+{
+    public class Archive : Popup
+    {
+
+        [Required(ErrorMessage = "Output file name is required")]
+        public string SaveFile
+        {
+            get => _saveFile;
+            set => SetProperty(ref _saveFile, value, true);
+        }
+
+        public object BasedOn
+        {
+            get;
+            private set;
+        }
+
+        public Archive(Repository repo, Models.Branch branch)
+        {
+            _repo = repo;
+            _revision = branch.Head;
+            _saveFile = $"archive-{Path.GetFileNameWithoutExtension(branch.Name)}.zip";
+            BasedOn = branch;
+            View = new Views.Archive() { DataContext = this };
+        }
+
+        public Archive(Repository repo, Models.Commit commit)
+        {
+            _repo = repo;
+            _revision = commit.SHA;
+            _saveFile = $"archive-{commit.SHA.Substring(0, 10)}.zip";
+            BasedOn = commit;
+            View = new Views.Archive() { DataContext = this };
+        }
+
+        public Archive(Repository repo, Models.Tag tag)
+        {
+            _repo = repo;
+            _revision = tag.SHA;
+            _saveFile = $"archive-{tag.Name}.zip";
+            BasedOn = tag;
+            View = new Views.Archive() { DataContext = this };
+        }
+
+        public override Task<bool> Sure()
+        {
+            _repo.SetWatcherEnabled(false);
+            ProgressDescription = "Archiving ...";
+
+            return Task.Run(() =>
+            {
+                var succ = new Commands.Archive(_repo.FullPath, _revision, _saveFile, SetProgressDescription).Exec();
+                CallUIThread(() =>
+                {
+                    _repo.SetWatcherEnabled(true);
+                    if (succ)
+                        App.SendNotification(_repo.FullPath, $"Save archive to : {_saveFile}");
+                });
+
+                return succ;
+            });
+        }
+
+        private readonly Repository _repo = null;
+        private string _saveFile = string.Empty;
+        private readonly string _revision = string.Empty;
+    }
+}