LMS-1511 use merged stream to deliver screening images

screening/build/build.xml

.../openbis/dss/screening/server/DssServiceRpcScreening.java

.../dss/screening/shared/api/v1/IDssServiceRpcScreening.java

...lugin/screening/client/api/v1/ScreeningClientApiTest.java

...creening/client/api/v1/ScreeningOpenbisServiceFacade.java

...gin/screening/shared/api/v1/dto/ImageDatasetMetadata.java

...ugin/screening/shared/api/v1/dto/PlateImageReference.java

.../plugin/screening/shared/api/v1/dto/PlateSingleImage.java