WIP Add support for custom torrents' approval storages

* migrate torrentapproval to list storage
* add initial support for torrent file storage (watch directory with fsnotify)
* replace frontend/http/bencode package with github.com/zeebo/bencode module
* sanitize code (fix warnings)

TODO:
* parse torrent files to get hashes,
* watch directory event types

DON'T use for now

middleware/pkg/random/xorshift.go

@@ -7,7 +7,7 @@ package random
 func GenerateAndAdvance(s0, s1 uint64) (v, newS0, newS1 uint64) {
 	v = s0 + s1
 	newS0 = s1
-	s0 ^= (s0 << 23)
+	s0 ^= s0 << 23
 	newS1 = s0 ^ s1 ^ (s0 >> 18) ^ (s1 >> 5)
 	return
 }