persistence: fixed tons of things, read the full description
persistence: fixed tons of things, read the full description

- value returned from last_insert_rowid() is now checked
- INSERT OR IGNORE INTO torrents is removed in favour of explicitly checking if the torrent is in the database
- changed trigger names for keeping 'torrents_idx' up to date
- fixed 'modified_on' once again, but this time for sure (it seems...)
boramalper/magnetico,boramalper/magnetico,boramalper/magnetico