Call downloader.Delete() for state files

[AskAlexSharov]

todo left:

• I changed onChange hook: from names list to relative paths list (need to check if this is what downloader expecting)
• To check if downloader.Del called and removed from lib

Not in todo:

• correct notifications about new files (it's less distractive)

Will continue work on it tomorrow

[sudeepdino008]

Looks good!
so as far as i understand:

• onFilesChange(nil) in a bunch of places can be populated later; it only delays new files getting seeded, which is fine.
• but onFilesDelete is more important as in, we must pass right value so they're removed from downloader and aren't resurrected.