Replace socket.io with plain WebSocket using the ws library as it
doesn't really provide any useful tools over plain WebSocket when it
comes to implementing reliable communication that works across
reconnects. The widespread browser support for WebSocket also means
it has little value to add for the web interface over WebSocket.
Remove connection and client subclasses of Link and put the connection
logic into a "connector" class. The connector deals with sending
and receiving messages, handling the connection and reconnection of lost
connections and giving sequence numbers to messages.
This move the logic of the actual connection away from the link
sub-classes, which in turn means the connection should be a lot easier
to mock in tests.
Hornwitser