SCUBA2: rename CSO entry as tau225

The CSO heading in the log files was causing some confusion, as it's
not actually derived from the CSO monitor values any more. Instead,
use a more generic heading called tau225 to be more explicit about
what it represents. Also update the corresponding POD to clarify that
the optical depths are those at the zenith.
PICARD: CSO heading is now Tau225

See previous commit for corresponding SCUBA2 primitives.
SCUBA2: fix a couple of indentation/spacing issues