Conservation of NumPy arrays and Spectral Bands

- new function extractSciSig() runs apsum on
non-2D-background-subtracted science images to produce the "true" sky
(band 3) and sigma (band 4) spectra. These 2 spectral bands are then
transferred to the 2D-background-subtracted extracted science spectra
(bands 3 and 4).
- The apsum-extracted science spectra (*aps) are kept and added to the
apsumsciences global dictionary.
- The extractSciSig() function is callable as an individual task.
- New 0-header keyword 'RUFAINT' has a value 0 if the user indicated
that the spectrum in the 2D image did not look faint, or a value of 1
otherwise.
- New 0-header keyword 'RUSIGMA', if present, gives the name of the
corresponding apsum-extracted science image.
- New function run_apsumSci() added to supplement new function
extractSciSig()