Allow developers to swap the socket client

[swentel]

We can now easily send a message to a relay, great!

But maybe folks don't like the client we use, so give them the option to swap it.

[Sebastix]

Found these two websocket client packages which seems to be useable besides the current one (https://github.com/sirn-se/websocket-php):

• https://github.com/ratchetphp/Pawl
• https://github.com/amphp/websocket-client