BIS-1096: Update on how properties with plugins are managed

...systemtest/plugin/excelimport/ImportDatasetTypesTest.java

...temtest/plugin/excelimport/ImportExperimentTypesTest.java

.../systemtest/plugin/excelimport/ImportSampleTypesTest.java

...celimport/test_files/sample_types/with_dynamic_script.xls

...c/server/xls/importer/helper/DatasetTypeImportHelper.java

...erver/xls/importer/helper/ExperimentTypeImportHelper.java

...r/xls/importer/helper/PropertyAssignmentImportHelper.java

...ic/server/xls/importer/helper/SampleTypeImportHelper.java

...eneric/server/xls/importer/helper/ScriptImportHelper.java

...penbis/generic/server/xls/importer/utils/ImportUtils.java