External trackers list support, info-dictionary receiving speedup for magnet links by early trackers client init

Now we can use manual trackers list to speedup peers finding. Which accelerates start of downloading and with early trackers client init info-dictionary receiving.

```
engine('magnet://...', 
	{trackers: [
		'udp://tracker.openbittorrent.com:80',
		'udp://tracker.ccc.de:80',
		'udp://tracker.istole.it:80',
		'udp://tracker.publicbt.com:80'
	]});
```