XLS ingestion service, with integration tests

...bis/systemtest/plugin/excelimport/AbstractImportTest.java

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

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

.../systemtest/plugin/excelimport/ImportExperimentsTest.java

...bis/systemtest/plugin/excelimport/ImportProjectsTest.java

...ystemtest/plugin/excelimport/ImportPropertyTypesTest.java

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

...nbis/systemtest/plugin/excelimport/ImportSamplesTest.java

...enbis/systemtest/plugin/excelimport/ImportSpacesTest.java

...temtest/plugin/excelimport/ImportVocabularyTypesTest.java

.../sis/openbis/systemtest/plugin/excelimport/TestUtils.java

...t/plugin/excelimport/test_files/dataset_types/no_code.xls

...in/excelimport/test_files/dataset_types/no_properties.xls

...n/excelimport/test_files/dataset_types/normal_dataset.xls

.../excelimport/test_files/dataset_types/with_validation.xls

...lugin/excelimport/test_files/experiment_types/no_code.xls

...limport/test_files/experiment_types/normal_experiment.xls

...rt/test_files/experiment_types/with_validation_script.xls

...ugin/excelimport/test_files/experiments/all_elsewhere.xls

.../plugin/excelimport/test_files/experiments/all_inside.xls