Fixed tests of the StructuresImporter: - Added test to verify behaviour when canceling at the two stages during the import. Test regarding cancelling while Creating structures is missing - Reverted changes related to HandleUserCancellingImport: messages are written by the LogImportCanceledMessage and handled adequately by the base Adjusted test in PipingSoilProfilesImporterTest - Changed initial value of the result to make clear that the value is set correctly Related to Issue [WTI-490]