Add ZMQ interface for BitcoinD

[bennyhodl]

Create the ZMQ interfaces and expose them through BitcoinD

Moved this upstream because I created a utility for LND and needed to add a function to retrieve the ZMQ interface.

[bennyhodl]

Bump @RCasatta

[RCasatta]

Thanks for the bump, I missed it.

Absolutely concept ack but I think we should add a config.enable_zmq or similar for enabling zmq which is false by default. My fear is using too many ports...

[bennyhodl]

@RCasatta added an optional config. Can rebase if it looks good

[RCasatta]

LGTM,
if you can squash and run cargo fmt

You can ignore CI error on windows, and also ignore clippy warnings.

[RCasatta]

ACK f69adc1