SCUBA2: fall back on date-obs/end FITS headers for elapsed time

PICARD doesn't know about the DURATION_SCIENCE uhdr, so just use the
DATE-OBS and DATE-END FITS headers to get the elapsed time.

In addition, a different file has to be chosen when called from
PICARD, assumed to be as part of the CHECK_RMS recipe. PICARD does not
know about "reduced" images, so use either the "calib" or "newimage"
data depending on whether or not the data needed calibrating before
analyzing.

The usual caveat applies that this will given nonsense results for
coadds/mosaics.
SCUBA2: use uncalibrated image in PICARD

In PICARD the "newimage" file is the input file, which may be
calibrated, so explicitly select the uncalibrated file before
proceeding with the analysis.
PICARD: swap calibrate/crop steps, write mapstats log file

In order to write out the correct values in the mapstats log file, the
caibration and cropping steps need to be reversed. This is because
mapstats operates on the whole image, not the cropped version.
PICARD: write out calstats log file as well

At some point this recipe will probably switch over to just writing
the calstats log file (and porbably undergo a name change at the same
time) but for now just write as many log files as desired and worry
about getting the right one later.