Provide "Restart Now" functionality

And use it for the plugin dialog and when changing the UI language.

Change-Id: Ic767837d2526409f7ec46d7e4612a1499f19459e
Reviewed-by: hjk <hjk@qt.io>
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/coreplugin/mainwindow.h

@@ -108,6 +108,8 @@ public:
 
     void saveSettings();
 
+    void restart();
+
 public slots:
     void openFileWith();
     void exit();