Use parameterMap::saveNexus re #4963

Signed-off-by: Karl Palmen <karl.palmen@stfc.ac.uk>
Move code from ExperimentInfo to Instrument re #4963

Signed-off-by: Karl Palmen <karl.palmen@stfc.ac.uk>
Merge remote-tracking branch 'origin/feature/4963_instrument_save_nexus'