db: refactor find_location()
db: refactor find_artist()
db: refactor add_new_artist()
db: refactor add_new_location()
db: refactor find_album()
db: refactor add_new_album()
db: refactor find_genre()
db: refactor add_new_genre()
db: refactor find_comment()
db: refactor add_new_comment()
db: refactor find_year()
db: refactor add_new_year()
db: refactor add_new_track()
db: refactor update_track()
db: refactor forget_track()
db: refactor find_playlist()
db: refactor find_radio()
db: refactor add_new_radio()
db: refactor add_radio_track()
db: refactor add_new_playlist()