LMS-1965, LMS-1973 fix overlays rescaling, use composition to draw transparent overlays

.../systemsx/cisd/etlserver/DefaultDataSetInfoExtractor.java

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

...emsx/cisd/openbis/dss/generic/shared/utils/ImageUtil.java

...systemsx/cisd/openbis/dss/etl/AbsoluteImageReference.java

.../systemsx/cisd/openbis/dss/etl/IImagingDatasetLoader.java

...cisd/openbis/dss/etl/dataaccess/ImagingDatasetLoader.java

...openbis/dss/generic/server/images/ImageChannelsUtils.java

...generic/server/images/dto/ImageChannelStackReference.java

...bis/dss/generic/server/images/dto/RequestedImageSize.java

...bis/dss/generic/server/images/ImageChannelsUtilsTest.java

...nbis/dss/screening/server/DssServiceRpcScreeningTest.java