Notice when Halflife websocket goes away

[tripleee]

If the websocket disappears, PulseMonitor should notice, and perhaps try restarting.

Currently, it looks like it simply keeps listening to the old, now dead websocket forever if Halflife is restarted.

There is also the scenario of Halflife dying, so it should probably not attempt to restart too often if the websocket cannot be opened in the first place.

[tripleee]

When I shut down Halflife for an update yesterday, there was a log message.

2018-06-05 12:24:34,136:WebsocketListener:A websocket error occurred on websocket 'ws://ec2-52-208-37-129.eu-west-1.compute.amazonaws.com:8888/':
2018-06-05 12:24:34,136:WebsocketListener:Connection is already closed.

https://chat.stackexchange.com/transcript/message/44984344#44984344