* Introduced FileImporterBase to allow for additional NotifyObserver calls to be done on UI thread when done importing. ** Moved responsibility for NotifyObserver on import target from FileImportActivity to FileImporterBase. ** Updated all existing importers to inherit from FileImporterBase. * Implemented additional logic for dealing with new ReferenceLine, when one was already available. Related to Issue [WTI-364] git-svn-id: https://repos.deltares.nl/repos/WettelijkToetsInstrumentarium/trunk@2177 5a3db67b-de53-47b5-99c8-a1c30a6650e2