LMS-823 ETL: make marker files optional

...msx/cisd/common/utilities/IDelegatedActionWithResult.java

datastore_server/dist/etc/service.properties

datastore_server/etc/service.properties

...ver/source/java/ch/systemsx/cisd/etlserver/ETLDaemon.java

...er/source/java/ch/systemsx/cisd/etlserver/Parameters.java

...rce/java/ch/systemsx/cisd/etlserver/ThreadParameters.java

...ch/systemsx/cisd/etlserver/TransferredDataSetHandler.java

...ystemsx/cisd/etlserver/TransferredDataSetHandlerTest.java