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/StashChanges.cs

@@ -0,0 +1,69 @@
+using System.Collections.Generic;
+using System.Threading.Tasks;
+
+namespace SourceGit.ViewModels
+{
+    public class StashChanges : Popup
+    {
+
+        public string Message
+        {
+            get;
+            set;
+        }
+
+        public bool CanIgnoreUntracked
+        {
+            get;
+            private set;
+        }
+
+        public bool IncludeUntracked
+        {
+            get;
+            set;
+        }
+
+        public StashChanges(Repository repo, List<Models.Change> changes, bool canIgnoreUntracked)
+        {
+            _repo = repo;
+            _changes = changes;
+
+            CanIgnoreUntracked = canIgnoreUntracked;
+            IncludeUntracked = true;
+            View = new Views.StashChanges() { DataContext = this };
+        }
+
+        public override Task<bool> Sure()
+        {
+            var jobs = _changes;
+            if (CanIgnoreUntracked && !IncludeUntracked)
+            {
+                jobs = new List<Models.Change>();
+                foreach (var job in _changes)
+                {
+                    if (job.WorkTree != Models.ChangeState.Untracked && job.WorkTree != Models.ChangeState.Added)
+                    {
+                        jobs.Add(job);
+                    }
+                }
+            }
+
+            if (jobs.Count == 0)
+                return null;
+
+            _repo.SetWatcherEnabled(false);
+            ProgressDescription = $"Stash changes ...";
+
+            return Task.Run(() =>
+            {
+                new Commands.Stash(_repo.FullPath).Push(jobs, Message);
+                CallUIThread(() => _repo.SetWatcherEnabled(true));
+                return true;
+            });
+        }
+
+        private readonly Repository _repo = null;
+        private readonly List<Models.Change> _changes = null;
+    }
+}