SCUBA2: don't display the last noise data in a focus observation

The display from the final noise in a focus observation was
overwriting the focus display too quickly. Therefore avoid displaying
any noise data in the QL and SUMMIT pipelines for subscans other than
the first.
SCUBA2: add KEEP parameter to allow recipe-specific suffices
SCUBA2: use tags to denote which data to use to make a map

Use data that is not tagged with "olddata" to make a map. Once that
data has been used, it is tagged with "olddata". This means that the
multi-level use of the "isgood" method can be phased out.
SCUBA2: pick the last sequence start/end values

The code designed to catch short sequences and so trigger map-making
needs to be told to pick the last element of the array to determine if
the sequence is a short one.
SCUBA2: need to keep _cal for now too in the SUMMIT pipeline
docs: refer to PAL instead of SLA.

The TELESCOPE header in question appears to be handled
by Astro::Telescope using PAL instead of SLA.
SCUBA2: use the noise at the peak for amplitude error if none exists

If the FIXAMP recipe parameter is specified, the error on the fitted
amplitude is, by definition, zero. However, in this case we can use
the noise at the peak position which was determined previously when
calculating the peak signal-to-noise.
SCUBA2: ensure log files can be read by Topcat

Topcat uses the last line before the data as the column headings. The
horizontal line put in by this primitive meant that the headings were
being ignored. The solution is to simply leave out that line.
SCUBA2: placeholders for FTS pointing and focus.
SCUBA2: only calculate the noise if a new image was created

In the summit pipeline, the log file log.noise had redundant entries
where the pipeline was still calculating the noise and writing it to
the log even though no new map had been created. Now just skip the
calculation unless a new image was created.
Index: abort from scanindex early if index is empty.

This avoids having to set up the filters if we have no results
to which to apply them.  It should prevent the :SINCE filter from
issuing a warning if an index file is empty.
SCUBA2: deal with case where there are no good bolometers from setup

If the setup fails, the flatfield ramps will return zero good
bolometers. In this case we can still write out the names of the
flatfield files to a flag file, but issue an error stating that it
will be incomplete.

Furthermore, it is not possible to write or update a badbol file if
there are no good bolometers. Let the existing list be used instead.
SCUBA2: add option to trim image to default map size

Running a source finder on an image runs the risk of detecting false
sources near the edge of the mapped area. In this case it may be more
appropriate to trim the map first, especially in cases where the
number of sources is small and expected to lie somewhere near the map
centre.

Add the CROP parameter which indicates whether the current map should
be trimmed before running the source finder. The default is false. If
true, then the pipeline uses the default map size as given in the
header.
SCUBA2: run a basic source finder on the group image
SCUBA2: calibrator obs wait to end to make map to ensure good FCFs

In order to ensure that the SUMMIT pipeline is calculating the best
possible FCFs, we wait until the observation has ended and make a map
using all data.