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/AddRemote.cs

@@ -0,0 +1,107 @@
+using System.ComponentModel.DataAnnotations;
+using System.Threading.Tasks;
+
+namespace SourceGit.ViewModels
+{
+    public class AddRemote : Popup
+    {
+        [Required(ErrorMessage = "Remote name is required!!!")]
+        [RegularExpression(@"^[\w\-\.]+$", ErrorMessage = "Bad remote name format!!!")]
+        [CustomValidation(typeof(AddRemote), nameof(ValidateRemoteName))]
+        public string Name
+        {
+            get => _name;
+            set => SetProperty(ref _name, value, true);
+        }
+
+        [Required(ErrorMessage = "Remote URL is required!!!")]
+        [CustomValidation(typeof(AddRemote), nameof(ValidateRemoteURL))]
+        public string Url
+        {
+            get => _url;
+            set
+            {
+                if (SetProperty(ref _url, value, true))
+                    UseSSH = Models.Remote.IsSSH(value);
+            }
+        }
+
+        public bool UseSSH
+        {
+            get => _useSSH;
+            set => SetProperty(ref _useSSH, value);
+        }
+
+        public string SSHKey
+        {
+            get;
+            set;
+        }
+
+        public AddRemote(Repository repo)
+        {
+            _repo = repo;
+            View = new Views.AddRemote() { DataContext = this };
+        }
+
+        public static ValidationResult ValidateRemoteName(string name, ValidationContext ctx)
+        {
+            if (ctx.ObjectInstance is AddRemote add)
+            {
+                var exists = add._repo.Remotes.Find(x => x.Name == name);
+                if (exists != null)
+                    return new ValidationResult("A remote with given name already exists!!!");
+            }
+
+            return ValidationResult.Success;
+        }
+
+        public static ValidationResult ValidateRemoteURL(string url, ValidationContext ctx)
+        {
+            if (ctx.ObjectInstance is AddRemote add)
+            {
+                if (!Models.Remote.IsValidURL(url))
+                    return new ValidationResult("Bad remote URL format!!!");
+
+                var exists = add._repo.Remotes.Find(x => x.URL == url);
+                if (exists != null)
+                    return new ValidationResult("A remote with the same url already exists!!!");
+            }
+
+            return ValidationResult.Success;
+        }
+
+        public override Task<bool> Sure()
+        {
+            _repo.SetWatcherEnabled(false);
+            ProgressDescription = "Adding remote ...";
+
+            return Task.Run(() =>
+            {
+                var succ = new Commands.Remote(_repo.FullPath).Add(_name, _url);
+                if (succ)
+                {
+                    SetProgressDescription("Fetching from added remote ...");
+                    new Commands.Fetch(_repo.FullPath, _name, true, SetProgressDescription).Exec();
+
+                    if (_useSSH)
+                    {
+                        SetProgressDescription("Post processing ...");
+                        new Commands.Config(_repo.FullPath).Set($"remote.{_name}.sshkey", SSHKey);
+                    }
+                }
+                CallUIThread(() =>
+                {
+                    _repo.MarkBranchesDirtyManually();
+                    _repo.SetWatcherEnabled(true);
+                });
+                return succ;
+            });
+        }
+
+        private readonly Repository _repo = null;
+        private string _name = string.Empty;
+        private string _url = string.Empty;
+        private bool _useSSH = false;
+    }
+}