code_review: PR #1185

- make `SourceGit` running in singleton mode
- `TrySendArgsToExistingInstance` should not be called before `BuildAvaloniaApp().StartWithClassicDesktopLifetime(args)` since we may want to launch `SourceGit` as a core editor.
- avoid `preference.json` to be saved by multiple instances.
- move IPC code to models.

Signed-off-by: leo <longshuang@msn.cn>

src/ViewModels/Preferences.cs

@@ -90,12 +90,6 @@ namespace SourceGit.ViewModels
             }
         }
 
-        public bool OpenReposInNewTab
-        {
-            get => _openReposInNewTab;
-            set => SetProperty(ref _openReposInNewTab, value);
-        }
-
         public bool UseSystemWindowFrame
         {
             get => _useSystemWindowFrame;
@@ -369,6 +363,11 @@ namespace SourceGit.ViewModels
             set => SetProperty(ref _lastCheckUpdateTime, value);
         }
 
+        public void SetCanModify()
+        {
+            _isReadonly = false;
+        }
+
         public bool IsGitConfigured()
         {
             var path = GitInstallPath;
@@ -496,7 +495,7 @@ namespace SourceGit.ViewModels
 
         public void Save()
         {
-            if (_isLoading)
+            if (_isLoading || _isReadonly)
                 return;
 
             var file = Path.Combine(Native.OS.DataDir, "preference.json");
@@ -632,13 +631,13 @@ namespace SourceGit.ViewModels
         private static Preferences _instance = null;
         private static bool _isLoading = false;
 
+        private bool _isReadonly = true;
         private string _locale = "en_US";
         private string _theme = "Default";
         private string _themeOverrides = string.Empty;
         private string _defaultFontFamily = string.Empty;
         private string _monospaceFontFamily = string.Empty;
         private bool _onlyUseMonoFontInEditor = false;
-        private bool _openReposInNewTab = false;
         private bool _useSystemWindowFrame = false;
         private double _defaultFontSize = 13;
         private double _editorFontSize = 13;