Move handling of color dialog that is opened from mode selector

It doesn't really make sense to have that handling deep in the
FancyTabWidget.

Change-Id: If4b4b9b9c3cbc49c25091982b398fb18f9bf87c2
Reviewed-by: Alessandro Portale <alessandro.portale@theqtcompany.com>

src/plugins/coreplugin/fancytabwidget.h

@@ -162,6 +162,7 @@ public:
 signals:
     void currentAboutToShow(int index);
     void currentChanged(int index);
+    void topAreaClicked(Qt::MouseButton button, Qt::KeyboardModifiers modifiers);
 
 public slots:
     void setCurrentIndex(int index);