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/DropStash.cs

@@ -0,0 +1,29 @@
+using System.Threading.Tasks;
+
+namespace SourceGit.ViewModels
+{
+    public class DropStash : Popup
+    {
+        public Models.Stash Stash { get; private set; }
+
+        public DropStash(string repo, Models.Stash stash)
+        {
+            _repo = repo;
+            Stash = stash;
+            View = new Views.DropStash() { DataContext = this };
+        }
+
+        public override Task<bool> Sure()
+        {
+            ProgressDescription = $"Dropping stash: {Stash.Name}";
+
+            return Task.Run(() =>
+            {
+                new Commands.Stash(_repo).Drop(Stash.Name);
+                return true;
+            });
+        }
+
+        private readonly string _repo;
+    }
+}