optimize<Preference>: show a dialog to confirm restart request

src/Resources/Locales/en_US.xaml

@@ -415,6 +415,9 @@
     <sys:String x:Key="Text.Conflict.Revert">Revert merge request detected! Press 'Abort' to restore original HEAD</sys:String>
     <sys:String x:Key="Text.Conflict.Merge">Merge request detected! Press 'Abort' to restore original HEAD</sys:String>
 
+    <sys:String x:Key="Text.Restart.Title">NOTICE</sys:String>
+    <sys:String x:Key="Text.Restart.Content">Restart required to apply changes in preference. Restart now?</sys:String>
+    
     <sys:String x:Key="Text.NotConfigured">Git has NOT been configured.\nPlease to go [Preference] and configure it first.</sys:String>
     <sys:String x:Key="Text.PathNotFound">Path[{0}] not exists!</sys:String>
     <sys:String x:Key="Text.MissingBash">Can NOT locate bash.exe. Make sure bash.exe exists under the same folder with git.exe</sys:String>

src/Resources/Locales/zh_CN.xaml

@@ -415,6 +415,9 @@
     <sys:String x:Key="Text.Conflict.Revert">检测到回滚提交冲突！</sys:String>
     <sys:String x:Key="Text.Conflict.Merge">检测到分支合并冲突！</sys:String>
 
+    <sys:String x:Key="Text.Restart.Title">系统提示</sys:String>
+    <sys:String x:Key="Text.Restart.Content">本次配置变更需要在重启后生效，是否立即重启？</sys:String>
+
     <sys:String x:Key="Text.NotConfigured">GIT尚未配置。请打开【偏好设置】配置GIT路径。</sys:String>
     <sys:String x:Key="Text.PathNotFound">路径（{0}）不存在或不可读取!</sys:String>
     <sys:String x:Key="Text.MissingBash">无法找到bash.exe，请确保其在git.exe同目录中！</sys:String>

src/Views/Preference.xaml.cs

@@ -121,7 +121,18 @@ namespace SourceGit.Views {
                 useDarkTheme != general.UseDarkTheme ||
                 checkUpdate != general.CheckForUpdate ||
                 autoFetch != general.AutoFetchRemotes) {
-                App.Restart();
+                var result = MessageBox.Show(
+                    this,
+                    App.Text("Restart.Content"),
+                    App.Text("Restart.Title"),
+                    MessageBoxButton.OKCancel,
+                    MessageBoxImage.Question,
+                    MessageBoxResult.Cancel);
+                if (result == MessageBoxResult.OK) {
+                    App.Restart();
+                } else {
+                    Close();
+                }
             } else {
                 Close();
             }