add maintenance option : db deduplication
dedicated db convert error code
allows using multiple db files at the same time
get table size
move old db away and create fresh
add torrent name to known hashes
add get torrent name from cache
factored sample parsing
use cached data for json list
db maintenance: data deduplication

useful for databases populated before the following
commit: 205d6aa3701a8395a12f85ee6add7de73d471bd2
ie release 1.0 and 1.1
Merge branch 'db-maintenance'