Store Chromaprint of a song

Finding Chromaprint of a song is an expensive process. We may need the chromaprint of a song many times, so store it in tracker db to be able to directly extract.

We could also store acoustid in tracker db, but I think it would be better to store chromaprint instead, because our acoustid grilo plugin retrieves metadata based on chromaprint and not acoustid.

Closes: #113 (closed)