PICARD: add support for user-specified FCF
PICARD: new recipe for calibrating SCUBA-2 data

By default this recipe will use the standard SCUBA-2 BEAM FCF to
calibrate the input files. The user may provide their own calibration
parameters using the recipe parameters FCF and FCF_CALTYPE (which may
be BEAM or ARCSEC). Calibrated output files have a suffix of _cal.

Files are only calibrated if the units are pW.