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/RenameBranch.cs

@@ -0,0 +1,66 @@
+using System.ComponentModel.DataAnnotations;
+using System.Threading.Tasks;
+
+namespace SourceGit.ViewModels
+{
+    public class RenameBranch : Popup
+    {
+        public Models.Branch Target
+        {
+            get;
+            private set;
+        }
+
+        [Required(ErrorMessage = "Branch name is required!!!")]
+        [RegularExpression(@"^[\w\-/\.]+$", ErrorMessage = "Bad branch name format!")]
+        [CustomValidation(typeof(RenameBranch), nameof(ValidateBranchName))]
+        public string Name
+        {
+            get => _name;
+            set => SetProperty(ref _name, value, true);
+        }
+
+        public RenameBranch(Repository repo, Models.Branch target)
+        {
+            _repo = repo;
+            _name = target.Name;
+            Target = target;
+            View = new Views.RenameBranch() { DataContext = this };
+        }
+
+        public static ValidationResult ValidateBranchName(string name, ValidationContext ctx)
+        {
+            if (ctx.ObjectInstance is RenameBranch rename)
+            {
+                foreach (var b in rename._repo.Branches)
+                {
+                    if (b != rename.Target && b.Name == name)
+                    {
+                        return new ValidationResult("A branch with same name already exists!!!");
+                    }
+                }
+            }
+
+            return ValidationResult.Success;
+        }
+
+        public override Task<bool> Sure()
+        {
+            if (_name == Target.Name)
+                return null;
+
+            _repo.SetWatcherEnabled(false);
+            ProgressDescription = $"Rename '{Target.Name}'";
+
+            return Task.Run(() =>
+            {
+                var succ = Commands.Branch.Rename(_repo.FullPath, Target.Name, _name);
+                CallUIThread(() => _repo.SetWatcherEnabled(true));
+                return succ;
+            });
+        }
+
+        private readonly Repository _repo = null;
+        private string _name = string.Empty;
+    }
+}