BIS-713: Amended value objects to reflect new specification, minor improvements

...s/custom-services/imaging/lib/openBIS-premise-imaging.jar

...s/generic/dssapi/v3/dto/imaging/ImagingDataSetConfig.java

.../generic/dssapi/v3/dto/imaging/ImagingDataSetControl.java

...ssapi/v3/dto/imaging/ImagingDataSetControlVisibility.java

...s/generic/dssapi/v3/dto/imaging/ImagingDataSetExport.java

...is/generic/dssapi/v3/dto/imaging/ImagingDataSetImage.java

.../generic/dssapi/v3/dto/imaging/ImagingDataSetPreview.java

...c/dssapi/v3/dto/imaging/ImagingDataSetPropertyConfig.java

...is/generic/server/dss/plugins/imaging/ImagingService.java

...r/dss/plugins/imaging/adaptor/IImagingDataSetAdaptor.java

...plugins/imaging/adaptor/ImagingDataSetExampleAdaptor.java

.../plugins/imaging/adaptor/ImagingDataSetJythonAdaptor.java

.../plugins/imaging/adaptor/ImagingDataSetPythonAdaptor.java

...gins/imaging/1/dss/custom-services/imaging/nanonis_dat.py

...gins/imaging/1/dss/custom-services/imaging/nanonis_sxm.py

...gins/imaging/1/dss/custom-services/imaging/spmpy_terry.py