Implement DiffSpec mode for OSIRIS diffraction algorithm. Refs #6791

This is not exposed to the GUI yet.
Use MSGReducer for OSIRIS diffspec mode. Refs #6791

Reorganised OSIRIS parameter files to follow IRIS/TOSCA. The interface
now uses the same MSGReducer for diffspec mode and only uses the workflow
algorithm for diffonly mode.
Remove DiffSpec mode from OSIRISDiffractionReduction.

Leave it doing diffraction only in favour of MSGReducer covering
spectroscopy mode. Refs #6791
Make rebin parameters optional on IndirectDiffractionReduction GUI

Refs #6791
Make the rebin string optional in indirect diffraction reduction.

If not given, RebinToWorkspace is used to rebin the workspace to the
first spectrum so that grouping can proceed.
Refs #6791
Rebin larger workspace of sample/vanadium to smaller.

Allows for a point where raw files started being written with an extra bin
and so could not be used with an earlier vanadium.
Refs #6791
Merge remote-tracking branch 'origin/feature/6791_osiris_diffspec_mode'