GDA (8.38.mt cherry pick from master) Changed NexusDataWriter to use SrsDataFile object when writing srs files. *Still needs work*

Breaks some functionality. May be restored for 8.40. See TODO in class.

Conflicts:
	uk.ac.gda.core/src/gda/data/scan/datawriter/NexusDataWriter.java
Changed SRS metadata class to allow reading from "metashop" collection instead of using its own internal collection
8.38 temporary fix until GDA-5974 is done.
Changed roi (HardwareTriggerableDetectorDataProcessor (DetectorDataProcessor.py)) .getDescription(), getDetectorID() and getDetectorType() to return " " instead of an empty string so we could write Nexus Files.
Removed the listing of metadata when from meta_add and meta_rm (works very badly when used in scripts).
Fixed NXMetaDataProvider to better handle PyIntegers when creating group data.
GDA (8.38.mt 8.38 ONLY) Fix GDA-5956 - Deadlock in scan shutdown - Paul G has a better plan for master and 8.40