add: support for channel-selection and page-selection images to method...

add: support for channel-selection and page-selection images to method loadImages() of screening API
change: always return a TIFF file in the screening API, if necessary, convert
fix: add authorization checks to forgotten methods listImageMetadata() and loadImages() in screening DSS RPC interface
change: rename method AbstractDssServiceRpc.assertDatasetsAreAccessible() to AbstractDssServiceRpc.checkDatasetsAuthorization() to make it clear the method is involved in authorization checking

SVN: 17313