Performance updates (#9082)

* Avoid creation of curve legend widgets during construction of a multi plot
* Make sure default z-value is correct to avoid expensive Qwt updates
* Avoid duplicate plot updates
* Do not create internal Qwt legend by default
* RFT import: Avoid expensive method throwing exception if no data is found

ApplicationLibCode/UserInterface/RiuSummaryQwtPlot.cpp

@@ -108,7 +108,9 @@ RiuSummaryQwtPlot::RiuSummaryQwtPlot( RimSummaryPlot* plot, QWidget* parent /*=
     RiuQwtPlotTools::setCommonPlotBehaviour( m_plotWidget->qwtPlot() );
     RiuQwtPlotTools::setDefaultAxes( m_plotWidget->qwtPlot() );
 
-    m_plotWidget->setInternalLegendVisible( true );
+    // PERFORMANCE NOTE
+    // Do not set internal legends visible, as this will cause a performance hit.
+    m_plotWidget->setInternalLegendVisible( false );
 
     m_annotationTool = std::unique_ptr<RiuPlotAnnotationTool>( new RiuPlotAnnotationTool() );
 }