Does a few things:
1) Adds gotaglib to third_party. If you'd like to review that, feel
free, though there's a bit of organization I'd like to do first.
2) Adds an "audioTag" key type.
3) Indexes wholerefs by various audio tags. Doesn't yet add a map from
wholeref to tags, but I can add that next.
Change-Id: I8e2a5bc27260086bad3351ac57973d1ac23cff44
Hunter Freyer