Add some basic contact information in a new Help->Contact dialog

Change-Id: I5a01c3d3c9fd467ed7b48869b66617adf2b11fed
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@qt.io>
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/coreplugin/mainwindow.h

@@ -129,6 +129,7 @@ private:
     static void setFocusToEditor();
     void aboutQtCreator();
     void aboutPlugins();
+    void contact();
     void updateFocusWidget(QWidget *old, QWidget *now);
     NavigationWidget *navigationWidget(Side side) const;
     void setSidebarVisible(bool visible, Side side);