Add "intrinsic" plot option (Galactic extinction correction and absolute mag/rest-frame day using distance)

[franzebauer]

It would be extremely valuable to add a plot option to explorer that

• allow inputs for distance in pc or redshift, Galactic extinction, and perhaps zero point day
• these would ideally populated with best values from cross-match...parallax distances/limits for Galactic sources or redshifts for extragalactic sources, and extinction from Schlegel maps
• or empty if some values from the match remain unpopulated
• plots extinction corrected absolute magnitudes and rest-frame days relative to zero point day (t=0 outburst time for transients)