PICARD: add PICARD uhdr so primitives know this is a PICARD recipe
SCUBA2: append suffix if called from PICARD

The standard pipeline approach to naming output files, whereby a new
suffix replaces the current one, is less desireable in PICARD where
preservation of the suffices makes the history unambiguous. Add a
check for the PICARD uhdr and, if present, simply append the suffix to
the current file name.
SCUBA2: KEEP_NEFD changed to WRITE_NEFD

WRITE_NEFD seems like a better name for this parameter as it implies
the NEFD image is written out somewhere.
PICARD: update due to changes in API in primitives called

In one case, an argument has been deleted, and in the other a
parameter has been renamed.
PICARD: no need to loop over files as Frame only contains 1

In PICARD, Frame objects only contain a single file so there is no
need to loop over multiple files.

Add a new output message informing the user of the uncalibration
action, and tag Frame contents with uncal.