Add loggers in lib/log.js

Winston library used for logging.
Two loggers added, tracker and indexer
Don't send back peers when stopped event recieved

Change some logs and fix bug in tracker.js:85-87
Fix info.pieces encoding problem

Problem was when decoding torrent file, pieces is given as buffer of bytes. But when converted to string or saved in db as string the encoding causes problems in length of pieces string (which according to BitTorrent specs should be counted as ascii bytes not unicode)
To fix it changed info.pieces type in TorrentData schema to buffer