Refactor ingest_spectral_types function

[kelle]

Should be just for one spectral type, not for a list of them.

Change:

n_added = 0
n_skipped = 0

to a flags dictionary with added and skipped keys.

flags = {'added': 0, 'skipped': 0}
if <added>:
    flags['added'] = 1
if <skipped>:
     flags['skipped]=1
...
return flags

[kelle]

We want to get this done so Austin can use it in #482 .