imaging: Provide image trimming for vignetting with UIST.
UIST: Add vignetting to the instrument hello script.
ifu: Create representative spectrum and preview images.

Remove the superfluous second _sp extension from the product name
for simplicity and consistency with other Archive products.
ifu: Create representative white-light image and preview images.

Remove the superfluous second _im extension from the product
name for simplicity and consistency with other Archive products.
ifu: Typos and use file format code in prologue.
ifu: Add licence.
ifu: Rework creating PRODUCT keywords and representative products.

Avoid creating the temporary representative product name without
the duplicated _im and _sp that are used elsewhere in the IFU recipes.
Thus _im_fc becomes _fci and _sp_fc becomes _fcs.

Separate the plain _im/_sp PRODUCT from the corresponding
flux-calibrated equivalent.  It uses internal header FLUX_CALIBRATED
but could look for _fc in the file name.
ifu: Remove the temporary _fci/_fcs file used to make rimg and rsp.
ifu: Fix typos.
ifu: Add FLUX_CALIBRATED flag in internal header.

This could be unnecessary, instead searching for the presence of _fc
in file names, but this approach seemed more robust.
ifu: Set the PRODUCT headers for the three flux-calibrated products.
ifu: Add further PRODUCT headers.
ifu: Add licence to recently modified primitives.