Show progress bar when appending plots to multiplot (#8976)

* Show progress bar when appending plots to multiplot
* Stop plot manager from going crazy creating plots when filter text is blank
* Speed up plot manager create plot

ApplicationLibCode/ProjectDataModel/RimMultiPlot.h

@@ -69,6 +69,9 @@ public:
     void removePlot( RimPlot* plot ) override;
     void movePlotsToThis( const std::vector<RimPlot*>& plots, int insertAtPosition );
 
+    virtual void startBatchAddOperation();
+    virtual void endBatchAddOperation();
+
     virtual void removePlotNoUpdate( RimPlot* plot );
     virtual void updateAfterPlotRemove();
 
@@ -169,6 +172,8 @@ protected:
     friend class RiuMultiPlotBook;
     QPointer<RiuMultiPlotBook> m_viewer;
 
+    bool m_delayPlotUpdatesDuringBatchAdd;
+
 private:
     caf::PdmChildArrayField<RimPlot*> m_plots;