SCUBA2: replace IMAGE with TAG as input parameter

The whitening will take place on the image tagged with the given TAG
rather than simply the given filename. This allows greater flexibility
and avoids the use of special keywords for the IMAGE parameter.
SCUBA2: do not store files in current Frame

This commit largely reverts b4323dfa15 as I discovered an issue in
PICARD whereby the input list of files contained the original input
files, which resulted in those files being added to the intermediates
list of the current Frame and were therefore being deleted at the end
of processing.

However, all is not lost - the list of files in the current Frame is
still used as the default input list.
SCUAB2: tag jack-knife map with "jackknife_map"

The input state is restored on exit.

Also move some code within the check for enough files to proceed.
SCUBA2: minor change in feedback to user
SCUBA2: terminate processing in not given a PSF in PICARD

The user must provide a PSF when this primitive is called from a
PICARD recipe. Terminate the recipe if none was given.
SCUBA2: no need to localise Grp, use tags instead

Use tags to store and retrieve the relevant files rather than
localizing Grp.

Also the output filenames for the matched filtered and signal-to-noise
maps are specified here so they can be easily deleted at the end of
processing.
SCUBA2: tag all members of Group before mosaicking

This allows the input state of each member of the Group to be restored
at the end of processing.

There is also no longer any need to delete files in the group after
mosaicking since the Group object is not localized.
SCUBA2: perform jack-knife noise check before processing science data

This might allow problems to be spotted before proceeding with the
science data.
PICARD: keep PSF image created, delete whitened jack-knife

These changes bring the recipe into line with the corresonding ORAC-DR
recipe.