Focus the newly dropped dock widget

When we drag a dock widget into a another widget, we should focus it

Fixes issue #77

src/private/MultiSplitter_p.h

@@ -188,10 +188,13 @@ public:
     Layouting::Item *itemForFrame(const Frame *frame) const;
 
     /**
-     * @brief Returns a list of Frame objects contained in this layout
+     * @brief Returns this list of Frame objects contained in this layout
      */
     QList<Frame*> frames() const;
 
+    /// @brief Returns the list of dock widgets contained in this layout
+    QVector<DockWidgetBase*> dockWidgets() const;
+
     /// @brief restores the dockwidget @p dw to its previous position
     void restorePlaceholder(DockWidgetBase *dw, Layouting::Item *, int tabIndex);