ifu: Improve mosaic-making efficiency.

Rather than create a mosaic from scratch for all of the cubes made thus
far, form a mosaic from the current mosaic cube with the pair of cubes
from the current quad.  The variance should take care of the weighting
although the zero pint would be better processing all the data.  Under
the former arrangement for n quads there would be 2*n*(n-1) operations
for MAKEMOS; under the new arrangement it's 3n.

Also the WCSFRAME calls that bracket the MAKEMOS step are invoked one
for each quad rather on average n.

To do this an extra steering header QUAD_CYCLE is added to select the
subgrp for the current quad.
ifu: Miscellaneous tidying.
ifu: Update the prologue.

Correct the product suffix, update the author list, and add
the licence.
ifu: Report all the files being mosaicked on the current cycle and in toto.

It had previously reported the last cube, not the last pair for the
quad.  Also an earlier change just listed the pair being added, not
the complete set of cubes that have been used to created the
groupfile, as did previously before 5f9a31140508f.
ifu: Remove changes to the WCS Frames.

MAKEMOS only uses pixel co-ordinates so make the code even more
efficient than switching WCS Frames in single calls (5f9a31140508f5)
by junking them altogether.  Also remove the change to the PIXEL
domain for the group file, which has the additional benefit of the
final spectral cube having sky co-ordinates rather than pixels along
its spatial dimensions.
general: Improve efficiency making preview images.

Rather than process each resolution separately, allow a series of
resolutions to be specified.  Restructure the code so that certain
calculations are factorised from their original location.  Also
default YRES to XRES if it undefined.
JSA: Take advantage of the more efficient way to compute multiple previews.
heterodyne: Report velocity range for the 90% summation.

In the no-retrieve mode or when the limits were not recovered, rather
than write out zeroes for the velocity limits in the log.standard,
instead use the actual limits.  In practice they will be
distinguishable from limits obtained from the standards' table because
they will not be round numbers and have two decimal places.

These should be distinct from the velocity ranges read from the
heterodyne: Remove no-retrieve call to _CALCULATE_STANDARD_.

Brad and Jan can offer no reason why there is a second call to
_CALCULATE_STANDARD_ with RETRIEVE false.  This just confuses matters
when there are two log.standard entries for the same object, one
summed of the emission region in the table just enclosing the emission
line, and a second summed over 90% (although it was not was clear over
what range the second flux was measured, now rectified by
05d29cea9483c).
heterodyne: Correct grammar.