#8370: Address review comments

Keep original additional summary files on Save As, reject cases combined with ensembles, keep unrestored additional file mappings, support growing file sets, update short names on ensemble import, simplify aggregator and example.

ApplicationLibCode/ProjectDataModelCommands/RimcSummaryMultiPlot.cpp

@@ -55,6 +55,11 @@ std::expected<caf::PdmObjectHandle*, QString> RimcSummaryMultiPlot_appendSubplot
 
     auto multiPlot = self<RimSummaryMultiPlot>();
 
+    if ( !m_summaryCases().empty() && !m_ensembles().empty() )
+    {
+        return std::unexpected( "Specify either summary cases or ensembles, not both." );
+    }
+
     RimSummaryPlot* newPlot = RimcSummaryPlotCollection_newSummaryPlot::createSummaryPlot( m_summaryCases.ptrReferencedObjectsByType(),
                                                                                            m_ensembles.ptrReferencedObjectsByType(),
                                                                                            m_addressString() );