Further Summary Multiplot improvements (#8707)

* Create a specialized summary plot page for showing multi plots
* Make summary plots always show in grid of selected size.
* Allow dragging summary addresses into empty main window area
* Limit grid to 4x4 cells

ApplicationLibCode/UserInterface/RiuPlotMainWindow.h

@@ -98,6 +98,8 @@ public:
 protected:
     void closeEvent( QCloseEvent* event ) override;
     void keyPressEvent( QKeyEvent* ) override;
+    void dragEnterEvent( QDragEnterEvent* event ) override;
+    void dropEvent( QDropEvent* event ) override;
 
 private:
     void setPdmRoot( caf::PdmObject* pdmRoot );