SCUBA2: restrict peak s/n check to same area as fit

The peak S/N check was being made on the whole image as given, which
sometimes led to spuriously high S/N values probably when a noisy edge
pixel was being treated as the peak. Instead, restrict the check to an
area equal to the fit box size.
SCUBA2: add gamma to list of returned parameters

Only bother with the first entry, not the uncertainty as that is all
that's needed to distinguish between 1 and 2-component fits.
SCUBA2: store aperture radius used for FCF calculation

The aperture radius used for the FCF calculation is stored in the
Frame uhdr under FCF_APERTURE_RADIUS to allow downstream primitives to
recall this number.
SCUBA2: remove errfrac from beam parameters

The errfrac entry in the beam parameters was never defined and has
always been stored as 0.
SCUBA2: add names of new log files, mapstats and calstats
SCUBA2: store the FCF uncertainty plus the measured flux & uncertainty

It's useful to know the measured flux from which the FCF was
derived. Store its uncertainty and the resultant uncertainty in the
FCF as well.
Calib: major updates to handling of SCUBA-2 beam parameters

The Calib::SCUBA2 module has been overhauled to produce a consistent
set of methods that deal with fits to the beam. This has resulted in
numerous updates:

 * methods have been grouped correctly by type - accessor methods
   dealing with the class attributes, instance methods dealing with
   instance variables

 * the FWHMfit and FWHMerr attributes replace the former somewhat
   vague FWHM entry

 * the beamarea method now uses an instance variable to return
   standard values, like the FCFs and beam parameters

 * beamfit method has been overhauled to store the relevant fit
   parameters

 * the fwhm_fit and errbeam methods have been updated in line with the
   beamfit updates

 * two new methods have been added: fwhm_err - to retrieve the FWHM of
   the error beam, and beamcomp - return the number of components in
   the fit to the beam
SCUBA2: new primitive for writing calibrator analysis results to log file

This primitive writes out the results of the FCF and beamsize
calculations carried out on a known calibrator.