SANS: Set the moderator to sample distance to that in the nexus/raw file

[mantid-builder]

Original Reporter: Steve Williams

Could we use the moderator to sample distance stored in the nxs file, as an alternative to the one in the idf ? This would bring Mantid in line with the historic practise in COLETTE. Would need to have a command in the mask file to activate this, else we would have some horrible backward compatibility issues. e.g. SAMPLEDIST/NXS or /RAW and SAMPLEDIST/IDF [default] SAMPLE/OFFSET would apply in all cases, though the value for this should hopefully be zero for /NXS if the instrument scientist has fed the correct value into the nxs file via SECI.

This distance should be reported in the Geometry tab.

The sample to detector distance shouldn't be changed by this setting!

[mantid-builder]

This issue was originally trac ticket 2791