Summary Multiplot: sync plot selection in tree with view (#8788)

* Make sure the subplot selected in the tree is shown in the multiplot viewer. 
* Clean up multiplot toolbar handling a bit
* Remove old summary plot toolbar.

ApplicationLibCode/Commands/RicImportSummaryGroupFeature.cpp

@@ -71,8 +71,7 @@ void RicImportSummaryGroupFeature::onActionTriggered( bool isChecked )
     if ( mainPlotWindow && !cases.empty() )
     {
         mainPlotWindow->selectAsCurrentItem( cases.back() );
-
-        mainPlotWindow->updateSummaryPlotToolBar();
+        mainPlotWindow->updateMultiPlotToolBar();
     }
 
     std::vector<RimCase*> allCases;