Use libtorrent-rasterbar to implement P2P download of mod files

[ngld]

Knossos will ask the user if they want to enable torrents during the first launch. This could save bandwidth on the mirrors and improve reliability during traffic spikes.

Each torrent will be automatically generated on the server and include web seeds to ensure that it will always be available (as long as we have mirrors, anyway).

This might require me to add a lot of new options to the settings view. (UL speed, listen port (random?), max DL speed, seed ratio, etc.)