Rename ExternalData to AbstractDataSet.

...ce/java/ch/systemsx/cisd/etlserver/DataStrategyStore.java

.../java/ch/systemsx/cisd/etlserver/IAutoArchiverPolicy.java

...temsx/cisd/etlserver/SmartParentDataSetInfoExtractor.java

...ch/systemsx/cisd/etlserver/api/v1/PutDataSetExecutor.java

...sd/etlserver/api/v1/PutDataSetTopLevelDataSetHandler.java

...emsx/cisd/etlserver/path/PathInfoDatabaseFeedingTask.java

.../ch/systemsx/cisd/etlserver/plugins/AutoArchiverTask.java

...temsx/cisd/etlserver/plugins/DummyAutoArchiverPolicy.java

.../cisd/etlserver/plugins/ExperimentBasedArchivingTask.java

...erver/postregistration/ArchivingPostRegistrationTask.java

...postregistration/Hdf5CompressingPostRegistrationTask.java

...stemsx/cisd/etlserver/postregistration/NotifyingTask.java

...ver/postregistration/PostRegistrationMaintenanceTask.java

...ver/registrator/api/v1/impl/AbstractTransactionState.java

...sd/etlserver/registrator/api/v1/impl/ConversionUtils.java

...d/etlserver/registrator/api/v1/impl/DataSetImmutable.java

...d/etlserver/registrator/api/v1/impl/DataSetUpdatable.java

...erver/registrator/api/v1/impl/MetaprojectAssignments.java

...cisd/etlserver/registrator/api/v1/impl/SearchService.java

...ver/registrator/api/v2/impl/AbstractTransactionState.java