SCUBA2: make sure to load the relevant module

Using DateTime::Format::ISO8601 means "use"ing it...
SCUBA2: add user messages when running from PICARD

The convention I've been loosely following with PICARD is to write out
the primitive name if it is being called on to do something.
PICARD: add verbose flag, inform user of action only when proceeding
PICARD: add CALSOURCE flag to only process known calibrators
PICARD: only proceed for known calibrators

A future enhancement would be to override this with a suitable recipe
parameter.
SCUBA2: print correct units in log file

Make sure the units string passed to the log file is correct. Save a
little space by abbreviating beam/arcsec/pixel.
PICARD: new recipe for mapstats/calstats

This is a combined and simplified version of the SCUBA2_CHECK_CAL and
SCUBA2_CHECK_RMS recipes to perform the same calstats and mapstats
logging done by the pipeline.