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!
No problem with uTorrent 1.8.4 on Mac OS X. While I experienced that exact bug with Transmission 2.82 on Ubuntu.