Freshen up tracker branch

I merged it with upstream, also:

1) Fixed overlapping migrations.
2) Wrong content type (application/bittorrent instead of just binary).
3) Realized about a transmission client bug with magnets (https://trac.transmissionbt.com/ticket/5507).
4) Simplified view a bit.

Thanks!
You have just edited the current API. This api will be replaced in the coming months by the new API that I linked in the above post. Btw I will take care of adding `info_hash` and `magnet_url` to the new API.