#3339 Make order of summary curves in plot predictable.

* The issue is sorting on pointer address for ensembles and summary cases. Instead sort by name.
* The crucial changes are in RiaSummaryCurveDefinition.cpp, RimSummaryCase and RimSummaryCaseCollection.
* The rest of the changes are just fallout from changing the pure virtual method RimSummaryCase::caseName to be const. The rest just follows.
* RimGridSummaryCase::caseName does alter something, but this variable was already declared mutable.

ApplicationCode/ProjectDataModel/Summary/RimObservedData.cpp

@@ -50,7 +50,7 @@ RimObservedData::RimObservedData()
 //--------------------------------------------------------------------------------------------------
 /// 
 //--------------------------------------------------------------------------------------------------
-QString RimObservedData::caseName()
+QString RimObservedData::caseName() const
 {
     QFileInfo caseFileName(this->summaryHeaderFilename());