Reduction of calibration sequence

[ajmejia]

This PR implements routines to reduce the calibration sequence from LVM and create the master frames.

Main changes are:

• Implements metadata fetching for calibration sequence
• Implements a low-level function to preprocess and detrend frames
• Handling of std fiber individual exposures (partially; randomised exposures will be fully handled in a different PR)
• Implements dome and twilight flats reduction to produce traces and fiberflats
• Implements arcs reduction to produce wavelength calibration frames