update SOLR on mp3 state changes (with a little refactoring)

server/djrandom/database.py

server/djrandom/fingerprint/cheap_dedup.py

server/djrandom/fingerprint/dedup.py

server/djrandom/fingerprint/resolve_duplicates.py

server/djrandom/frontend/frontend.py

server/djrandom/frontend/search.py

server/djrandom/model/indexer.py

server/djrandom/scanner/indexer.py

server/djrandom/scanner/scanner.py