Handle rate limiting for Ethereum websockets

[Mirko-von-Leipzig]

We currently use the Web3<WebSocket> transport for our Ethereum connections.

Using an Infura node can result in rate limiting. Currently web3 does not easily expose this error type - issue link.

We will want to deal with this, the easiest way is wrapping the transport and detecting the error manually. Alternatively, we can fork web3 and expose it. It may be worth forking if we get some feedback from the issue.

[CHr15F0x]

Closing for now since #140 is done and there is little benefit
in forking web3 at the moment while there are more pressing issues wrt API services.