Open Project: Don't show a error dialog for duplicated projects

Instead, switch to edit mode, show sidebar, scroll to project,
and show a tooltip next to the project.

The tooltip is somewhat easy to miss, but this is a clear improvement
in most cases.

Change-Id: Icd27f76e7d434f33e731b6fd56473ff913986a89
Task-number: QTCREATORBUG-8422
Reviewed-by: Eike Ziller <eike.ziller@theqtcompany.com>

src/plugins/coreplugin/navigationsubwidget.h

@@ -72,6 +72,8 @@ public:
     Command *command(const QString &title) const;
     void setCloseIcon(const QIcon &icon);
 
+    QWidget *widget();
+
 signals:
     void splitMe(int factoryIndex);
     void closeMe();