Use Websockets for Monitoring Services

[AusIV]

The current monitoring services (the exchange fill monitor and the block monitor) use HTTP polling to monitor for changes. This means:

• We have extra traffic going back and forth between services
• We can't trivially load-balance the monitoring services, because they need to talk to the same backend consistently.

Geth supports a websockets subscription endpoint that can provide the same information over a websockets connection, which would have less back-and-forth traffic, and would mean we could establish a connection with any available Ethereum node and it would be good for the life of the connection.

[AusIV]

This has been superceded by the new monitoring system we've put in place.