Swift WIP (compiles, but segfaults in tribler)

- Uses the same checkout as SwiftEngine submodule in Tribler.
- Uses the same precompiled libevent2 module as previous version because libevent2 recipe doesn't work.
- Segfaults when executed with the same arguments as tribler (swift -j -l 0.0.0.0:7758 -c 127.0.0.1:59907 -g 127.0.0.1:52493 -e /data/data/org.tsap.tribler.full/files/.Tribler/collected_torrent_files -T 180)