Perform flat correction

[mgalloy]

Flats applied to a science image must match specific criteria (from Paul):

In addition to exposure time and wavelength, there is the camera temperature. The camera also has gain and bit depth settings, but we do not expect these ever to change. Nonetheless, I think we should make these match too for future proofing and as an extra check.

Questions

• What do we do on days without the Kuhn-Lin flats? How exactly do we adjust the Kuhn-Lin flat using a "normal" flat?

Tasks

• Create dictionary of flats to be used for flat correction.
• Save this dictionary of flats in the calibration netCDF.
• Create ability to lookup the required flat for a science image.
• Apply the flat.