Replace TCP with Unix sockets

[bajtos]

We start the Lassie HTTP server listening on a TCP port now. This allows other processes to communicate with our Lassie instance.

A possible alternative is to rework the communication with Lassie to happen over a Unix socket (AF_UNIX), ideally an unnamed one.

Further reading about AF_UNIX support on Windows:

• golang/sys@fa5fdf9
• https://devblogs.microsoft.com/commandline/af_unix-comes-to-windows/
• https://stackoverflow.com/questions/9029174/af-unix-equivalent-for-windows#48053310