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!
@nimiq, can you try this magnet with your Transmission torrent when you have a moment? Oh, well, this one in fact, which is better formatted:

http://academictorrents.com/details/5fc2f273123336ee34b9ea635ef8440377a42888

Make sure you click on the "magnet" link, not the regular torrent download. Let me know if your client stalls in a similar way as it does in this transmission bug: https://trac.transmissionbt.com/ticket/5507