Quality assurance relative transparency plots for mmirs_qrp

[astrochun]

Using the differenced images, integrate the flux around bright target if available. Then compare these 1-D spectra to get relative transparency to the best image. Finally plot the relative transparency vs the exposure number.

[astrochun]

Began implementation with bright = True in 0494f7d. Need to normalize by exposure time and make sure the background subtraction is at zero.

[astrochun]

Exposure time normalization done in 9281e71. Plotting improvements done in b240bd9, cdd89a1, 66c25ee. Array containing total counts is normalized to unity for reference.

[astrochun]

Difficulty in background subtraction stems from using A-B difference images. We will need to avoid the region with the negative source.