Add support for displaying the apogee/aspcap model spectrum

[havok2063]

Beta test feedback. "Plot APOGEE/ASPCAP model spectrum + element windows in target view (similar to the old IR data viewer)"

Add support for displaying the model spectrum in the target page Jdaviz. Minimally we can add the spectrum to the list. More complicated is the overlay of line elements. Displaying line lists is a feature already in Jdaviz that users can use manually and do. Will need to think about whether this is something to punt to the user.