SCUBA2: primitives to track observation properties to compare with ITC

This trio of primitives form the basis of retrieving and logging
so-called "CHECK RMS" data, named after the PICARD recipe. In
practice, the aim is to store observational parameters along with
noise and NEFD values for processed images in order to compare with
the expectations from the integration time calculator (ITC).

Each primitive represents a particular step in the collection of these
data.

 * _GET_CHECKRMS_DATA_FROM_HEADER_ retrieves all the necessary
   information from the current Frame/Group header.

 * _GET_CHECKRMS_DATA_FROM_IMAGE_ retrieves the exposure time, noise
   and NEFD data from the current Frame/Group image (within a given
   aperture, default is 90" radius) and obtains the corresponding
   values from the ITC.

 * _WRITE_CHECKRMS_LOGFILE_ writes a log file (log.checkrms) with all
   the desired results.
PICARD: these steps have been factored out into separate primitives

These new primitives can be called directly in the CHECK_RMS recipe so
this primitive is no longer needed.
SCUBA2: add CHECK_RMS tracking to the SUMMIT pipeline

The SUMMIT pipeline - at least when processing science/pointing data -
will now keep track of variables such as the elapsed time, noise and
NEFD for the current coadd as well as corresponding values from the
SCUBA-2 integration time calculator. The results are written to a log
file, log.checkrms.
PICARD: call CHECK_RMS primitives directly

The old monolithic CHECK_RMS collection primitive has been factored
out into three separate primitives which describe the steps more
clearly. Therefore they can be called directly by this recipe and
there is no need to use an intermediate primitive.
SCUBA2: add checkrms as a known log file