Minor update of DT spreadsheets

I just made some cosmetic changes to the DT
spreadsheets (attached) - sorted out the formats.

I notice Sylvia/Gefeg deleted the SDT 'prefix' values.
Whilst I accept that these are not part of CCTS,
don't we still need these to be part of the UBL
DT spreadsheets? Likewise I'd note that the
SDT 'values' need to be added back once decided.

All the best

Steve